GB2142036A - Novel silyl compounds - Google Patents

Abstract

Novel silyl compounds of formula IIIA R<a>xSi(NCY)4-x IIIA wherein R<a> is selected from electron donating substituents including alkoxy, cycloalkoxy, aralkoxy, aryloxy, the group R<b>R<C>N-wherein R<b> and R<c> are selected from alkyl, cycloalkyl, aryl and aralkyl or R<b> and R<c> may be joined to form a heterocyclic ring with the nitrogen atom, alkylthio, cycloalkylthio, aralkylthio, arylthio and hydrocarbon substituents selected from alkyl, cycloalkyl, aralkyl or aryl, at least one group R<a> being an electron donating substituent, Y is oxygen or sulphur, x has a value from 1 to 3 with the provisos that (i) when x is 3 and all three R<a> groups are the same alkoxy then the alkoxy group has at least 3 carbon atoms; (ii) when R<a> is alkoxy and x is 1 then R<a> is other than propoxy; (iii) when one or more R<a> are alkylthio and the others (if any) are alkyl then the alkylthio group has at least 2 carbon atoms; (iv) when R<a> is aryloxy and x is 3 then at least one group R<a> is other than aryloxy, may be used in the preparation of fused carbocyclic ring derivatives of pyridine as described in Serial No. 2122615A. Preferred compounds of the invention are Dimethylisopropoxysilyl isothiocyanate and tri(dimethylamino)silyl isothiocyanate. s

Description

SPECIFICATION Novel silyl compounds The invention relates to novel silyl compounds and processes for preparing them. The compounds are useful in the process for preparing fused carbocyclic ring derivatives of pyridine, which process is described and claimed in our co-pending application 2122615A from which the present application is divided.

In our United Kingdom Patent Specification No. 1463666 we described a process for preparing tetrahydroquinoline-8-thiocarboxamides, nitriles and carboxamides and related compounds by treating a corresponding sodio, lithio, potassio or magnesium halide derivative with a silyl compound of formula RXSi(NCY)4 x wherein R is alkyl, aryl or aralkyl, Y is oxygen or sulphur and x has a value from 0 to 3 and subjecting the product to hydrolysis or alcoholysis. The reaction is conducted under anhydrous conditions preferably in an inert solvent for example a hydrocarbon solvent such as benzene, toluene or n-hexane. It is also stated in that patent specification that ethers, including cyclic ethers such as tetrahydrofuran should be avoided.

We have now surprisingly found that ethers can be used as solvents if the silyl reagent is modified to contain an alkoxy group or other electron donating substituent. Our new process, which is claimed in application 2122615A; can also be used to prepared compounds related to those described in Patent Specification 1463666. The new reagents can also be used in the same solvents described in UK Specification 1463666.

This invention concerns new silyl reagents, which may be used in the process of application 2122615A, and which are compounds of formula IIIA, RXSi(NCY)4 x wherein Ra is selected from electron donating substituents including alkoxy, cycloalkoxy, aralkoxy, aryloxy, the group RbRCN-wherein Rb and Rc are selected from alkyl, cycloalkyl, aryl and aralkyl or Rb and Rc may be joined to form a heterocyclic ring with the nitrogen atom, alkylthio, cycloalkylthio, aralkylthio, arylthio and hydrocarbon substituents selected from alkyl, cycloalkyl, aralkyl or aryl, at least one group Ra being an electron donating substituent, Y is oxygen or sulphur, x has a value from 1 to 3, with the provisos that (i) when x is 3 and all three Ra groups are the same alkoxy then the alkoxy group has at least 3 carbon atoms;; (ii) when Ra is alkoxy and x is 1 then Ra is other than propoxy; (iii) when one or more Ra are alkylthio and the others (if any) are alkyl then the alkylthio group has at least 2 carbon atoms; (iv) when Ra is aryloxy and x is 3 then at least one group Ra is other than aryloxy.

In general the preferred reaction medium for the process of the present invention comprises an ether solvent eg., a dialkyl ether, wherein the alkyl group has from 1 to 6 carbon atoms, eg., diethyl ether or a cyclic ether such as tetrahydrofuran or dioxan. Other reaction media which may be used are hydrocarbon solvents such as benzene, toluene, or n-hexane, or mixtures of two or more of the above mentioned solvents.

Preferably at least one electron donating group Ra is alkoxy of 1-10 carbon atoms, cycloalkoxy of 4-8 carbon atoms, aryloxy, aralkoxy of 7-1 2 carbon atoms or di(C1-C6 alkyl)amino. Good results have been obtained in the process of Serial No. 2122615A with a silyl compound of formula R3SiNCY wherein one group Ra is lower alkoxy or aryloxy and the other two are lower alkyl eg., methoxydimethylsilyl isothiocyanate isopropoxydimethylsilyl isothiocyan ate 2,6-d i-t-butyl-4-methylphenoxyd imethylsilyl isothiocyanate.

However two or all three of the Ra groups may be alkoxy eg., trimethoxy or triethoxy, or dialkylamino eg dimethylamino. Branched chain alkoxy or aryloxy groups are preferred. A particularly useful compound Ill is tri(dimethylamino)silyl isothiocyanate. Ra may have from 1-10 carbon atoms when alkyl or alkylthio.

When any of Ra, Rb or Rc is an alkyl radical it is preferred that this is a lower alkyl radical of 1 to 6 carbon atoms which may have a straight or branched chain eg., methyl, ethyl, n -and iso propyl and n, and t-butyl. When Ra is an alkoxy radical it is preferred that the radical is lower alkoxy in which the alkyl portion has 1 to 6 carbon atoms and is as defined above, for an alkyl radical. Similarly when Ra is an alkylthio group the alkyl portion is as defined for an alkyl group.

When any of Ra,Rb or Rc is a cycloalkyl radical such radicals having from 4 to 6 carbon atoms are preferred ie., cyclobutyl, cyclopentyl or cyclohexyl. If Ra is cycloalkoxy or cycloalkylthio the cycloalkyl portion of this group preferably has from 4 to 8 carbon atoms but may be as just described for a cycloalkyl group.

An aralkyl group may be an arylalkyl group in which the alkyl portion is as described herein for an alkyl group. Preferred aralkyl groups are those having from 7-1 2 carbon atoms.

An aralkyloxy group may be such a group in which the aralkyl portion is as just described for an aralkyl group. The aryl portion is preferably phenyl.

When any of Ra, Rb, or Rc is an aryl group it is preferably phenyl or substituted phenyl (substituted by eg., alkyl, alkoxy or trifluoromethyl). Similarly an aryloxy or arylthio group may be such a group in which the aryl portion is as defined for an aryl group, 2,6-disubstituted phenyl being a preferred group.

The silyl compounds of formula IIIA may be prepared by reacting a thiocyanate, such as ammonium thiocyanate, or a cyanate, with a silyl halide, RxSiHal4 x eg., R3SiHal where Ra is as defined above and Hal is chlorine or bromine.

Novel compounds of the invention include compounds of formula Illa, wherein one or two groups Ra are alkoxy or aryloxy and another group Ra is alkyl and x is 3 eg., Me2(0Me)SiNCS Me2(OiPr)SiNCS Me(OMe)2SiNCS 2,6, di-t-butyl-4-methylphenoxy (Me)2SiNCS and where one or more groups Ra are dialkylamino eg., (Me2N)3SiNCS.

The compounds of formula IIIA may be prepared by reacting a silylhalide RaSi(Hal)4 x, wherein Hal is chlorine, bromine or iodine, preferably chlorine, [Ra and x being as defined above with a thiocyanate eg., ammonium thiocyanate, or a cyanate. Methods of preparing the novel compounds of formula IIIA are included in the invention.

The silylhalides are known or may be prepared by methods known for analogous compounds.

The following Examples illustrate the invention.

Example 1 Preparation of silyl isothiocyanates General Method Ammonium thiocyanate (1.1 molar equivalents) in cyclohexane (100 ml) was refluxed with stirring under a Dean-Stark apparatus until water had been removed. The suspension was cooled and treated with a silyl chloride (50g) and the mixture was heated at reflux with stirring until the reaction was complete (usually 24 hours). Precipitated ammonium chloride was removed by filtration and the product purified by distillation.In this manner were prepared the following: Silyl chloride Silylisothiocyanate bp/mm Yield a) Me2(OMe)SiCl Me2(OMe)SiNCS 148"C/760 68% b) Me2(OiPr)SiCI Me2(OiPr)SiNCS 68"C/15 79% c) Me(OMe)2SiCI Me(OMe)2SiNCS 58"C/15 66% d) (Me2N)3SiCI (Me2N)3SiNCS 140'C/15 15% Example 2 Reaction of silylisothiocyanates with tetrahydroquinolines General Method A 5,6,7,8-tetrahydroquinoline (0.01 mole) in the solvent indicated (approx. 1 5 ml) at 0,C under nitrogen was treated with an alkyl lithium or a lithium amide (0.01 mole). To this solution of the 5,6,7,8-tetrahydro-8-lithioquinoline was added, at around O"C under nitrogen, the silyl isothiocyanate (0.01 mole) and the mixture was stirred 15 minutes. H20(10 ml) and 2N HCI (15 ml) were added and the acid layer was separated and washed with ethyl acetate. The aqueous solution was basified (Na2CO3) and extracted with chloroform.The chloroform extracts were dried (MgSO4) and evaporated to give the 5,6,7,8-tetrahydroquinoline-8-thiocarboxamide. in this manner the thioamides in the table were prepared.

I 15 Silyl Yield Expt, R Derivatives Solvent Base (a) 3-Me Me2Si(OMe)NCS THF n-BuLi 5% (b) 3-Me Me2Si(OiPr)NCS THF n-BuLi 30-35% (c) 3-Me Me2Si(OiPr)NCS toluene n-BuLi 15% -(d) 4-Me Me2Si(OiPr)NCS toluene n-BuLi 5% (e) 4-Me Me2Si(OiPr)NCS & THF n-BuLl 10% (f) 4-Me Me2Si(OiPr)NCS \\toiuene BU > Ntl 20% (g) 4-Me Me2Si(OiPr)NCS - THF 1 " ≈ 25% 1 I (h) 3-Me Me(OMe)2SiNCS THF ! n-BuLi 10% (i) 3-Me (Me2N)3SiNCS 1 THF n-BuLi n-BuLi| 40% (j) 3-Me / But ! THF | n-BuLi 50% Incus > Me2 ~ ~ 8ut 1

No product was obtained when the above reactions were carried out using Me3SiNCS in tetrahydrofuran (THF) instead of the named silyl derivative.

Example 3 a) 2, 6-Di4 -butyl-4-meth ylphenoxydimethylchlorosilane A mixture of 2,6-di-t-butyl-4-methylphenol (110g, 0.5M) acetonitrile (500 ml), triethylamine (70ml, 0.5M) and dichlorodimethylsilane (61my, 0.5M) was refluxed for 16 hours. The solvent was evaporated and the residue extracted with toluene (500 ml). The toluene extract was evaporated and the residue recrystallised from acetonitrile to give the title compound (90g, 57%) m.p. 119-121" (Found: C,65.65; H,9.4%. C,7H29 CLOSE requires C,65.2; H,9.3%).

b) 2, 6-Di4-butyl-4-methylphenoxydimethylsilyl isothiocyanate A mixture of the silyl chloride (789, 0.25M), ammonium thiocyanate (269, 0.28M) and toluene was refluxed for 48 hours. The mixture was filtered and the filtrate evaporated; recrystallisation of the residue from acetonitrile gave the title compound (409, 48%) m.p.83-4 . (Found: C,64.8; H,9.0; N,4.05. C,8H29 NOSSi requires C,64.4; H,8.7; 4.2).

Claims (12)

1. A compound of formula lIlA RXaSi(NCY)4 x IIIA wherein Ra is selected from electron donating substituents including alkoxy, cycloalkoxy, aralkoxy, aryloxy, the group RbRcN-wherein Rb and Rc are selected from alkyl, cycloalkyl, aryl and aralkyl or Rb and Rc may be joined to form a heterocyclic ring with the nitrogen atom, alkylthio, cycloalkylthio, aralkylthio, arylthio and hydrocarbon substituents selected from alkyl, cycloalkyl, aralkyl or aryl, at least one group Ra being an electron donating substituent, Y is oxygen or sulphur, x has a value from 1 to 3 with the provisos that (i) when x is 3 and all three Ra groups are the same alkoxy then the alkoxy group has at least 3 carbon atoms; (ii) when Ra is alkoxy and x is 1 then Ra is other than propoxy;; (iii) when one or more Ra are alkylthio and the others (if any) are alkyl then the alkylthio group has at least 2 carbon atoms; (iv) when Ra is aryloxy and x is 3 then at least one group Ra is other than aryloxy.

2. A compound of formula lIlA as claimed in Claim 1, wherein one or two groups Ra are alkoxy or aryloxy, another group Ra is alkyl and x is 3.

3. A compound of formula IIIA as claimed in Claim 2, wherein one or more groups Ra are dialkylamino.

4. Dimethylmethoxysilyl isothiocyanate.

5. Di methylisopropoxysilyl isothiocyanate.

6. Methyldimethoxysilyl isothiocyanate.

7. 2,6, Di-t-butyl-4-methylphenoxydimethylsilyl isothiocyanate.

8. Tri(dimethylamino)silyl isothiocyanate.

9. A process for preparing a compound of formula IIIA as claimed in any one of claims 1 to 3, which process comprises reacting a silylhalide RxaSi(Hal)4 xwherein Hal is chlorine, bromine or iodine, and Ra and x are as defined in Claim 1, 2 or 3, with a thiocyanate or a cyanate.

10. A process as claimed in Claim 9, substantially as hereinbefore described in Example 1.

11. A process as claimed in Claim 9, substantially as hereinbefore described in Example 3b.

12. A compound of formula lIlA, whenever prepared by a process as claimed in Claim 9, 10 or 11.