GB1591374A

GB1591374A - Heterocyclic hydroxy ketones and their use as herbicides

Info

Publication number: GB1591374A
Application number: GB3775976A
Authority: GB
Original assignee: INT DEV RES CENTER
Current assignee: INT DEV RES CENTER
Priority date: 1977-09-12
Filing date: 1977-09-12
Publication date: 1981-06-24

Description

(54) HETEROCYCLIC HYDROXY KETONES AND THEIR USE AS HERBICIDES (71) We, INTERNATIONAL DEVELOPMENT RESEARCH CENTRE, a public corporation organised and existing under the laws of Canada, having a principal office or place of business in the City of Ottawa, Ontario K16 3H9, Canada, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to novel compounds and to processes for the preparation of such compounds which are useful for the control of certain parasitic weeds. The invention also includes weed control compositions suitable for this purpose. More particularly the invention relates to novel compounds and herbicidal compositions prepared therefrom which are useful for controlling the weeds Striga hermonthica, S. asiatica (lute), Orobanche crenata, O. ramosa and O. aegyptiaca which are parasitic on certain economically important crops such as sorghum, maize, sugar cane and/or broad beans.

It is known that certain compounds and herbicidal compositions containing one or more of such compounds as an active ingredient thereof are useful in the control of parasitic weeds of the genera Striga and Orobanche. Some of these compounds suffer from the disadvantage that they tend to be slightly unstable in the locus where they are intended to be used as herbicides.

The present invention is based on the discovery that certain related novel chemical compounds possess improved stability or more effective herbicidal activity than the foregoing known compounds and they are able to act as effective germination stimulants for the seeds of Striga hermonthica, S. asatica, Orobanche crenata, O. ramosa and O. aegyptiaca.

According to the invention there is provided a compound of the formula:

wherein X represents a single bond or a -CH2- linkage, and wherein when R, and R2, which may be the same or different, stand for hydrogen, an alkyl radical of one to five carbon atoms or an aryl radical, substituted or unsubstituted, then R' and R" are joined, together with the adiacent two carbon atoms. to form a ring structure of the formula:

or wherein when R, and R2 are joined, together with the adjacent two carbon atoms, to form a rinz structure of the formula:

then R' and R", which may be the same or different, stand for hydrogen, an alkyl radical of one to five carbon atoms or an aryl radical, substituted or unsubstituted, or they may be joined, together with the two adjacent carbon atoms, to form a ring structure of the frarm l

wherein Y represents two hydrogen atoms to form a

group or an additional bond to form a

group, or an oxygen atom to form a

epoxy group.

R"' stands for hydrogen, an alkyl radical of one to five carbon atoms or an aryl radical, substituted or unsubstituted and the benzene rings A and B may be substituted by one or more substituents, the same or different, or one or both of the benzene rings A and B may have fused thereto a benzene ring or a heterocyclic ring.

As representative compounds of the invention there may be mentioned compounds corresponding to one of the formulae II, III, IV, V, VI and VII:

wherein Rl, R2, R', R", R"', X, Y, A and B have the meanings stated above.

As a particular substituent for the alkyl radical R1, R2, R', R" or R"' there may be mentioned a methyl, ethyl, n-propyl, isopropyl, n-butyl, sec.-butyl or tert.-butyl radical and of these, methyl is preferred. The substituent R1, R2, R', R" or R"' may be an aryl radical such as a phenyl or naphthyl radical optionally substituted by one or more alkyl, alkoxy or halogen radicals. The representation X is preferably a single bond and the representation Y is preferably an additional bond.

The benzene rings A and B may be substituted by one or more substituents selected from alkyl or alkoxy radicals of one to 8 carbon atoms, such as methyl, ethyl, propyl, butyl, methoxy, ethoxy, propoxy or butoxy, halogen such as chlorine or bromine, aryl, such as phenyl or naphthyl, or aralkyl, such as benzyl. As stated above, one or both of the benzene rings A and B may have fused thereto a benzene ring or a heterocyclic ring whereby the said benzene ring A and/or benzene ring B becomes enlarged to a naphthalene ring or a benzo-heterocyclic ring thus providing a compound of higher molecular weight.

Particularly useful compounds falling within the above stated formula are compounds represented by formulae IIA, IIIA, IVA, VA, VIA and VIIA as follows:

According to a further feature of the invention there is provided a process for the manufacture of a compound of the above stated formula I which comprises reacting a derivative of the enolic form of an a-formyl-butenolide represented by the formula IA:

with an appropriate butenolide derivative of the formula IB:

wherein R1, R2, R', R" and X have the meanings stated above and Z stands for a halogen atom, a methanesulphonate radical (CH3SO20-) or a tosylate radical (CH3C6H4.SO20-).

The said derivative of the enolic form of an a-formyl-butenolide is preferably a metallic derivative thereof in the form of a salt of the enol such as an alkali metal salt for example the sodium salt. Suitable salts for use in the preparation of the preferred compounds are the sodium-enolate salt of 3-hydroxymethylene-1,4-butyrolactone, the sodium-enolate salt of the zy-lactone of 4-hydroxycyclopentenyl-5-(a-formylacetic acid), the sodium-enolate salt of the zy-lactone of indan-2-ol-1-(a-formylacetic acid) and the sodium-enolate salt of the y-lactone of indan-1-ol-2-(a-formylacetic acid).

Á suitable synthesis for the preparation of the enol compound, in the form of its sodium salt, used as starting material for the preparation of compound IVA or VA is.as follows:

Suitable syntheses for the preparation of the enol compound, in the form of its sodium salt, used as starting material for the preparation of compound VIA or VIIA are as follows:

The said butenolide derivative, as stated above, may be in the form of the methanesulphonate or a tosylate or in the form of a halogen derivative such as the chloro derivative (Z = Cl) or the bromo derivative (Z = Br). Suitable butenolide derivatives for use in preparation of the preferred compounds are 3-bromophthalide, 5chloro-3-methylbut-2-enolide, 3-methyl0-but-2-enolide-5-methanesulphonate and 3-methylbut-2-enolde-5-p-5oluensulphonate.

The said process may be conveniently carried out in the presence of a suitable solvent or diluent such as an organic solvent or diluent for example 1 ,2-dimethoxyethane. The process conveniently takes place at ambient temperature until reaction is complete and the period of reaction may be of the order of 15 to 20 hours.

It is to be understood that the compounds of the present invention may exist in different stereoisomeric forms. Each compound has an optically active centre in the right hand ring structure of its formula. In addition, any compound which has more than one ring in the left hand ring structure of its formula has a second chiral feature as illustrated by reference to the structure of compound IVA wherein the asymmetric centres are shown below:

In view of the cis fusion of the rings, the said compound may exist only in two diastereoisomeric forms which can be separated one from another. For example, compound IVA has been separated into its two diastereoisomeric forms, identified conveniently as the "slow" isomer and the "fast" isomer respectively according to the rate at which each isomer is eluted from a silica column (see Example 3 hereinafter). Each such diastereoisomeric form of the compound may be further separated into its dextrorotatory (D)-form and its laevorotatory (L)-form.

It is therefore to be further understood that the compounds of the present invention include all possible stereoisomeric forms of each compound.

According to a further feature of the invention, there is provided a method for controlling at least one of the parasitic weeds, Striga hermonthica, S. asiatica (lutea), Orobanche crenata, O. ramosa and 0. aegyptiaca which comprises contacting dormant seeds thereof with a compound corresponding to the formula I, wherein R" R2, R', R" and X have the meanings stated above.

In carrying out the method for controlling said weeds, it is generally preferred that the host plant, i.e. the plant on which the germinated weed seeds attach themselves and grow, is absent from the soil containing the parasitic weed seeds being treated, or that the host plant has substantially reached maturity so that any infestation of the host plant by the parasitic weed following germination of the seeds thereof will have a minimal effect on the host plant and harvesting of the latter or natural death at the end of the growing season will prevent the parasitic weed from reaching maturity and consequently re-seeding itself. It is however to be understood that the said method may conveniently be carried out at other periods during the life of the host plant. Thus, it may be convenient to carry out the said method using one of the compounds of the present invention in admixture with a selective herbicidal agent after the sowing of the host plant or during the period of active growth of the host plant.

It may also be advantageous to give the seeds of Orobanche or Striga species a preliminary treatment with a solution of gibberellic acid before treatment with one of the compounds of the present invention as a method of controlling these parasitic weeds.

The invention also consists in herbicidal compositions comprising as an active ingredient a compound of the formula I wherein Rl, R2, R', R" and X have the meanings stated above, in association with a suitable carrier or diluent therefor.

The compound of formula I is preferably applied to the soil containing the dormant parasitic weed seeds in the form of a composition containing the active compound in admixture with a suitable carrier or diluent. Suitable carriers or diluents are particularly finely divided solid inert carriers or diluents such as powdered chalk, powdered clays, or powdered conventional fertilizers. Also suitable are liquid carriers or diluents such as water or an organic liquid. Pre-mixes of a relatively high concentration of the active agent with a carrier may be formulated for ease of handling, particularly for ease in preparing the final herbicidal composition to be applied to the soil. For instance, such a pre-mix may take the form of a solution of the active compound in an inert organic solvent, such solution optionally containing a surface active agent selected to promote the formation of an aqueous emulsion when the concentrate is diluted with a large volume of water for application to the soil.

The active compound to be used in the above method for controlling weeds or the above herbicidal compositions is preferably a compound of formula II, III, IV, V, VI or VII. Such a compound may be applied to the soil containing the parasitic weed seeds in amounts of from 100 to 5000 grams/hectare or from 0.01 to 0.5 gram/cubic meter of soil, and for this purpose compositions may be used containing from 0.001 to 1000 parts per million of the active compound, the balance of such compositions being essentially diluent or carrier as described above. The actual concentration of the active compound is of little importance compared with its rate of application to the soil. Too little of the active compound.may secure insufficient germination of the parasitic weed seeds to afford effective control.

Naturally, temperature and moisture conditions in the soil should be suitable for the germination of the parasitic weed seed.

A more preferred compound to be used in the method for controlling the said weeds or to be used in the herbicidal compositions is a compound of the formula IIA, IIIA, IVA, VAs VIA or VIIA. Of these, the compounds presently of choice are the compounds of formulae IVA and VIA which are particularly effective against Orobanche crenata and Striga hermonthica.

It is known that a compound of the formula VIIIA:

is active as a germination stimulator and may be used as a herbicidal agent in the control of parasitic weeds of the genera Striga and Orobanche. In comparison with the known compound VIIIA, the preferred compounds IVA and VIA of the present invention show an improvement over the said compound VIIIA as germination stimulators in laboratory tests and it is expected that a comparable improvement or advantage will be obtained when the compounds of the present invention are used as herbicides against Striga and Orobanche weeds.

The invention is illustrated by, but not limited by, the following Examples: Example 1 Preparation of Compound (IIA)

A mixture of the sodium-enolate salt (0.87g) and 3-bromophthalide (1.07g) in anhydrous 1,2-dimethoxyethane (20 ml) was stirred at room temperature for 18 hours and then diluted with ice-cold water (80 ml). The precipitated solid product was collected and recrystallized from a mixture of dichloromethane and hexane. The product in the form of mixed diastereoisomers had m.p. 212-213 (Found: C, 67.6; H, 4.3; Cl6H,205 requires C, 67.6; H, 4.25).

Example 2 Preparation of Compound (IIIA)

3-Bromophthalide (1.07g) was added to a suspension of the sodium-enolate salt of 3-hydroxymethylene-1,4-butyrolactone (0.68g) in anhydrous 1,2-dimethoxyethane (15 ml) and the mixture stirred at room temperature for 18 hours. The mixture was then diluted with water (100 ml) and extracted with dichloromethane (3 x 30 ml). The combined organic extract was washed with water (50 ml) followed by saturated salt solution (50 ml), dried over sodium sulphate and evaporated to dryness. The solid residue crystallized from methylene chloride-hexane mixture as colourless needles, m.p. 185-189 . (Found: C, 63.45; H, 4.15; Cl3Hl005 requires C, 63.4; H, 4.05).

Example 3 Preparation of Compound (IV) (i) 2-Bromoindan-l-ol This was prepared from indene according to the known procedure. The n.m.r. spectrum in deuteriochloroform confirmed that the product was trans-2-bromoindan-1-ol.

(ii) Trans-indan-2-ol-1-acetic acid This was prepared by modification of the known procedure. Sodium (0.46g) was added in small pieces to a stirred solution of diethyl malonate (3.2g) in 1,2-dimethoxyethane (15 ml) at room temperature (3 hours). The resulting solution was treated with a solution of 2-bromoindan-1-ol (2.lug) in 1,2-dimethoxyethane (12 ml) and the mixture stirred at room temperature overnight. It was then heated under reflux for 1 hour, cooled and evaporated to dryness.

The mixture of crude diester and excess diethylmalonate was saponified by boiling with 2N sodium hydroxide (60 ml) for 1.5 hours. The resulting solution was cooled, washed with ethyl acetate (30 ml x 2), acidified with 6N hydrochloric acid and saturated with salt.

Continuous extraction with ether for 24 hours followed by removal of the solvent gave a solid product which crystallized from benzene-alcohol, when it had m.p. 116-118 .

The hydroxy-diacid was decarboxylated by heating in an oil bath to about 130 with stirring under an atmosphere of nitrogen for 1 hour. The resulting oil solidifed on cooling and was crystallized from benzene-hexane. It had m.p. 124-132 (Found: C, 68.6; H, 6.25; Cl,Hl203 requires C, 68.75; H, 6.25%). The n.m.r. spectrum of the compound clearly showed it to be trans-indan-2-ol-1-acetic acid; double irradiation studies at 220 MHz showed the presence of -CHrCH-CH-CH2- carbon skeleton, inconsistent with the previous structural assignment.

(iii) Lactonisation of trans-indan-2-ol-1-acetic acid The hydroxy-acid (2.5 g) (above) was dissolved in 65% concentrated sulphuric acid in acetic acid (10 ml) and kept at room temperature for 24 hours. It was then poured onto cracked ice (300 g) and the aqueous solution extracted with dichloromethane (60 ml x 4).

The combined organic extract was washed with water (100 ml x 2) followed by 5% sodium bicarbonate (50 ml x 2) and then saturated salt solution (30 ml). After drying over sodium sulphate, the organic solution was filtered and evaporated to give an oil which slowly crystallized. Recrystallization from dichloromethane-hexane mixture gave the desired lactone as colourless needles, m.p. 73-74 . (Found: C, 75.85; H, 5.75. CllHl002 requires C, 75.8; H, 5.7%).

(iv) Formylation of the lactone of indan-2-ol-1-acetic acid Sodium (0.23g) was added to a solution of the foregoing lactone (1.74g) in a mixture of ethyl formate (1.1 lg) and ether (20 ml) and the reaction stirred at room temperature for 18 hours. The light-tan sodium-enolate salt was filtered, washed quickly with a small amount of ether and dried overnight in a desiccator.

Preparation of Compound (ivy)

5-Chloro-3-methylbutenolide (0.66g) was added to a suspension of the foregoing sodium-enolate salt (1.12g) in anhydrous 1,2-dimethoxyethane (20 ml) and the mixture stirred for 16 hours. At the end of this period the mixture was diluted with water (50 ml) and extracted with chloroform (60 ml x 3). The combined chloroform extract was shaken with saturated salt solution, dried over sodium sulphate, filtered and evaporated to dryness.

The residual light brown solid was crystallized from chloroform-ether to give a colourless product (mixed isomers), m.p. 200-214 . (Found: C, 68.45; H, 4.85; Cl,Hl405 requires C, 68.45; H, 4.7. The product, which is a diastereoisomeric mixture, was separated on a silica column (activity III; 84 x 2.5 cm) eluting with 2% ethyl acetate in ether. The "slow" isomer which had the lower RF value on a silica plate, eluted with ethyl acetate-ether mixtures and had m.p. 205 . The "fast" isomer had m.p. 119-120 .

Example 4 Preparation of Compound (VA)

3-Bromophthalide (0.7g) was added to a suspension of the foregoing sodium-enolate salt (0.75g), prepared as for compound (IVA) above, in anhydrous 1,2-dimethoxyethane (15 ml) and the mixture stirred for 18 hours. At the end of this period the mixture was poured into ice (50g) and the solid product filtered and dried in desiccator. A further crop of the product was obtained by extracting the aqueous mother liquor from above with chloroform (30 ml x 3), the extract beig dried over sodium sulphate, filtered and evaporated to dryness. Crystallization from dichloromethane-hexane mixture gave a crystalline product (mixed diastereoisomers) m.p. 161-168 . (Found: C, 71.55; H, 4.28. C20Hl4Os requires C, 71.85; H, 4.19%).

Example 5 Preparation of Compound (VIA) Lactonisation of trans-indan-1-ol-2-acetic acid Trans-indan-1-ol-2-acetic acid (3.4g) was dissolved in 25% aqueous sulphruic acid (25 ml) and ether (150 ml) was added, the mixture being stirred vigorously at room temperature for 18 hours. The ether layer was separated, shaken with saturated salt solution (25 ml) and dried over sodium sulphate. Filtration and removal of the solvent in vacuo gave an oily product which crystallized on standing. Recrystallization from ether-light petroleum (b.p. 60-80 ) yielded the desired cis-lactone as colourless needles, m.p. 64-65 .

Formylation of the lactone of cis-indan-1-ol-2-acetic acid The foregoing cis-lactone (2.61g) was added to a suspension of sodium (0.345g) in anhydrous ether (50 ml) followed by ethyl formate (1.8 g) and anhydrous ethanol (1.0 ml).

The mixture was stirred at room temperature under nitrogen for 18 hours. The precipitated sodium-enolate salt was filtered, washed quickly with dry ether (25 ml) and dried overnight in a vacuum desiccator.

Preparation of Compound (VIA)

5-Chloro-3-methylbutenolide (0.663g) was added to a suspension of the foregoing sodium-enolate salt (1.12g) in anhydrous 1,2-dimethoxyethane (20 ml) and the mixture stirred for 19 hours. Crushed ice (40 g) was then added and the aqueous solution extracted with chloroform (60 ml x 4). The combined chloroform extract was washed with saturated salt solution (20 ml), dried over sodium sulphate, filtered and evaporated to dryness in vacuo. The crystalline solid so obtained was recrystallized from dichloromethane-hexane and gave compound (VIA) (mixed diastereoisomers as colourless needles, m.p. 116-124 .

(Found C, 68.45; H, 4.7. C17H14O5 requires C, 68.45; H, 5.05%).

Example 6 Preparation of Compound (VIIA)

A mixture of the sodium-enolate salt (0.75 g), prepared as for compound (VIA) above, and 3-bromophthalide (0.71g) in anhydrous 1,2-dimethoxyethane (10 ml) was stirred at room temperature for 19 hours. Ice (20g) was added and the crystalline solid so obtained was separated and dried. The product (mixed diastereoisomers) had m.p. 163-173 .

In order to demonstrate the activity of the compounds in promoting the germination of seeds of Striga hermonthica, Striga asiatica, Orobanche aegyptiaca, Orobanche crenata and Orobanche ramosa, the following method was used. Seeds of the parasitic weeds were first sterilized with a 1% aqueous sodium hydrochlorite solution for 10-15 minutes, and then washed with distilled water until free of hypochlorite.

The Striga and Orobanche seeds were pre-treated by incubating at 23 C under moist conditions, e.g. on moist glass fibre filter paper, for 10-14 days. Usually about 25 seeds on 10 mm discs of the filter paper were employed.

Discs carrying pre-treated seed of Striga or Orobanche were dabbed to remove surplus moisture. Two discs were then placed in each of two replicate dishes, so there were 4 discs per treatment, carrying a total of about 100 seeds. The compounds to be tested were dissolved in ethanol and diluted to the required concentration with distilled water. The amount of ethanol was never greater than 0.5%v/v in the final solution. Freshly prepared solutions were always used. To each disc was Table 1 Germination tests on Striga hermonthica Concentration %Germination (p.p.m.) Compound Compound (IIA) (IIIA) 100 32 33 50 43 39 10 35 25 5 38 17 1 29 1 0.5 30 6 0.1 0 16 Control (distilled water): 6% germination It will be seen that both compounds are active and compound (IIA) is more active than compound Table II Germination tests on Orobanche ramosa concentrtion %Germination (p.p.m).

Compound Compound Compound Compound (IIA) (IIIA) (IVA) (VA) 100 0 0 1 1 10 0 1 2 2 2 2 0 0 2 0.1 0 0 0 3 0.01 50 42 55 10 0 001 13 34 50 46 0 0001 30 21 50 9 Control (distilled water): 9% germination It will be seen that all four compounds are active and that compound (IVA) is the most active compound of the four compounds tested Table III Germination tests on Orobanche crenata Concentration %Germination (p.p.m.) Compound Compound Compound (IVA) (IVA) (VIIIA) ("slow" ("fast" moving moving isomer) isomer) 50 66 49 0.1 18 39 14 0.01 9 8 0 Control (distilled water): 0% germination It will be seen that there is no marked difference between the unresolved DL-paris of diastereoisomers (the "slow" and "fast" isomers) of compound (VIA). Each of these isomers is superior in activity to compound (VIIIA).

Table IV Germination tests on Orobanche crenata Concentration % Germination (p.p.m.) Compound Compound Compound (VIA) (VIIA) (VIIIA) 100 27 18 24 10 37 3 18 42 2 5 0.1 14 5 3 0.01 8 6 1 0.001 3 16 1 0.0001 1 5 0 Control (distilled water): 1% germination Each of the compounds (VIA) and (VIIA) is superior in activity to compound (VIIIA) over the lower range of concentration.

Table V Germination tests on Striga hermonthica Concentration % Germination (p.p.m.) Compound Compound Compound (IVA) (IVA) (VIIIA) ("slow" ("fast" moving moving isomer) isomer) 100 9 1 1 50 17 3 7 10 10 9 8 5 50 44 23 1, 60 28 24 0 5 44 10 18 0 1 7 19 12 0.05 8 20 28 0.01 10 22 21 Control (distilled water): 2% germination Both the "slow" moving isomer and the "fast" moving isomer of compound (IVA) show appreciable activity. Each of these isomers is superior in activity to compound (VIIIA) over certain ranges of concentration.

Claims

WHAT WE CLAIM IS: 1. A compound of the formula I:

wherein X represents a single bond or a -CH2- linkage, and wherein when R, and R2, which may be the same or different, stand for hydrogen, an alkyl radical of one to five carbon atoms or an aryl radical, substituted or unsubstituted, then R' and R" are joined, together with the adjacent two carbon atoms, to form a ring structure of the formula:

or wherein when R, and R2 are joined, together with the adjacent two carbon atoms, to form a ring structure of the formula:

then R' and R", which may be the same or different, stand for hydrogen, an alkyl radical of one to five carbon atoms or an aryl radical, substituted or unsubstituted, or they may be joined, together with the two adiacent carbon atoms to form a ring structure of the formula:

wherein Y represents two hydrogen atoms to form a

group or an additional bond to form a

CH CtI group, or an oxygen atom to form a

epoxy group.

R"' stand for hydrogen, an alkyl radical of one to five carbon atoms or an aryl radical, substituted or unsubstituted and the benzene rings A and B may be substituted by one or more substituents, the same or different, or one or both of the benzene rings A and B may have fused thereto a benzene ring or a heterocyclic ring.
2. A compound as claimed in claim 1 having the formula II, III, IV, V, VI or VII as follows:

wherein R" R2, R', R", R"', X, Y, A and B have the meanings stated in claim 1.
3. A compound as claimed in claim 1 or 2 wherein one or more of R" R2, R', R" and R"' is a methyl, ethyl, n-propyl, isopropyl, n-butyl, sec.-butyl or tert.-butyl radical.
4. A compound as claimed in claim 1 or 2 wherein one or more of R" R2 R', R" and R"' is methyl.
5. A compound as claimed in claim 1 or 2 wherein one or more of R" R2 R', R" and R"' is a phenyl or naphthyl radical optionally substituted by one or more alkyl, alkoxy or halogen radicals.
6. A compound as claimed in any preceding claim wherein X is a single bond.
7. A compound as claimed in any preceding claim wherein Y represents an additional bond.
8. A compound as claimed in any preceding claim wherein one or both of the benzene rings A and B is substituted by one or more substituents selected from alkyl or alkoxy radicals of one to 8 carbon atoms, halogen, aryl or aralkyl radicals.
9. A compound as claimed in claim 8 wherein one or both of the benzene rings A and B is substituted by one or more methyl, ethyl, propyl, butyl, methoxy, ethoxy, propoxy, butoxy, chlorine, bromine, phenyl, naphthyl or benzyl radicals.
10. A compound as claimed in Claim 2 wherein of R, and R2, one is methyl and the other is hydrogen, R"' is hydrogen and X is a single bond.
11. A compound which is represented by formula IIA, IIIA, IVA, VA, VIA or VIIA as follows: -
12. A process for the manufacture of a compound as claimed in claim 1 which comprises reacting a derivative of the enolic form of an a-formyl-butenolide represented by the formula IA:

with an appropriate butenolide derivative of the formula IB:

wherein R" R2, R', R" and X have the meanings stated in claim 1 and Z stands for a halogen atom, a methanesulphonate radical (CH3SO20-) or a tosylate radical (CH3C6H4.S020-) .
13. The process as claimed in claim 12 wherein the derivative IA is a metallic derivative thereof in the form of a salt of the enol.
14. The process as claimed in claim 13 wherein the salt is an alkali metal salt.
15. The process as claimed in Claim 14 wherein the salt is a sodium salt.
16. The process as claimed in claim 12 wherein the derivative IA is the sodium-enolate salt of 3-hydroxymethylene-1,4-butyrolactone, the sodium-enolate salt of the #-lactone of 4-hydroxycyclopentenyl-5-(α-formylacetic acid), the sodium-enolate salt of the #-lactone of indan-2-ol-1-(α-formylacetic acid) and the sodium-enolate salt of the -lactone of indan-l-ol-2-(cw-formyl-acetic acid) .
17. The process as claimed in any of claims 12 to 16 wherein the derivative IB is the chloro derivative (Z = C1) or the bromo derivative (Z = Br).
18. The process as claimed in any of claims 12 to 16 wherein the derivative IB is 3-bromophthalide, 5-chloro-3-methyl-but-2-enolide, 3- methylbut-2-enolide-5-methanesulphonate or 3methylbut-2-enolide-5-p-toluenesulphonate.
19. The process as claimed in any of claims 12 to 18 wherein the process is carried out in the presence of a suitable solvent or diluent.
20. The process as claimed in claim 19 wherein the process is carried out in the presence of 1,2-dimethoxyethane.
21. The process as claimed in any of claims 12 to 20 wherein the process is carried out at ambient temperature until reaction is complete.
22. The process according to claim 21 wherein the process is carried out for a period of 15 to 20 hours.
23. A method for controlling at least one of the parasitic weeds, Striga hermonthica, S. asiatica (lutea), Orobanche creanta, O. ramosa and O. aegyptiaca which comprises contacting dormant seeds thereof with a compound corresponding to the formula I, wherein R" R2, R', R" and X have the meanings stated in claim 1.
24. The method of claim 23 wherein the seeds of Orobanche or Striga species are given a preliminary treatment with a solution of gibberellic acid before treatment with one of the compounds of formula I.
25. The method of claim 23 or 24 wherein the compound used is a compound as claimed in any one of claims 2 to 10.
26. A herbicidal composition which comprises as an active ingredient a compound of the formula I wherein R" R2, R' and R" and X have the meanings stated in claim 1, in association with a suitable carrier or diluent therefor.
27. A composition as claimed in claim 26 wherein the active ingredient is a compound as claimed in any one of claims 2 to 10.
28. A compound according to claim 1 substantially as herein described.
29. A process according to claim 12 substantially as herein described with reference to any one of Examples 1 to 6.
30. A method according to claim 23 substantially as herein described.