FR2588554A1 - Process for the alkenylation of imines - Google Patents

Abstract

Process for the alkenylation of imines carrying a functional group alpha to their nitrogen atom by the action, on such an imine, of an olefinic radical, in the presence of a Pd or Pt compound as catalyst, in a solvent. The olefinic radical is in the form of a carbonate whose CO3 group is connected to the C atom of the olefin alpha to the double bond of the latter.

Description

 The present invention relates to the alkenylation of imines carrying a functional group in position i of their nitrogen atom. It is intended in particular imines whose second function is an ester, a nitrile or an amide. The invention relates primarily to a catalytic process of alkenylation and it also includes the new imines to which it provides access.

It is known to allyler ester-imines on the carbon atom at d of iminic nitrogen, when the ester group is carried by this same carbon, an allylic radical which is attached to this carbon atom is used for this purpose. ; such a reaction has been described in particular by
Gilbert STORK et al. in J.Org.Chem. vol. 41, no. 21, 1976, pages 3491-3493, by ELAD et al. in J.Amer.Chem.

Soc. 93, 1971, page 967 and by Martin J. O'DONNELL et al. in Tetrahedron Letters, vol. 23, No. 41, 1982, pages 4259 to 4262. However, this scientific work has not been of a nature to give rise to industrial achievements. A marked progress has been made in this direction by the design of a catalytic process, described in US Pat. French Patent No. 80 02053, which relates to the manufacture of imine derived from allylamino acid, by catalytic or stoichiometric allylation, in the presence of at least one compound of Pd or Pt, an imine derived from an ester of the glycine or other o (amino acid.

 The use of a palladium catalyst complexed with a phosphine has allowed, according to this patent, the allylation of ester-imines with a yield of up to about 55%, an interesting result given the usefulness of various esterimines, in particular. particular for obtaining the corresponding amino acids. Since alkenyl, attached to the carbon at eX of nitrogen, can be readily hydrogenated to an alkyl, it would thus be possible to obtain different alkylated amino acids.

 However, in spite of this progress, the search for a process capable of economical application to the preparation of a wide variety of imines, without limitation to esterimines, was essential. It was indeed important to push the yield to more advantageous values, as far as possible approaching 90%. On the other hand, since the prior methods require a basic medium for alkenylation, they not only include the expense of basic reagents, but substantially exclude the presence of groups other than ester in place thereof. Indeed, in basic medium, different functional groups, in particular -CN, NO2 or -CONH2, may be affected, decomposed or eliminated, with lowering of the yield in the desired imitate and formation of secondary products. Ester groups themselves are vulnerable in such an environment because of their saponification.

 The present invention overcomes these shortcomings of the prior art: it allows alkenylation with greatly improved yields, amounting to 60 to 90%, depending on the case, on the initial imitation, and this within a solvent containing no base. In addition, this alkenylation can be carried out not only on the imines carrying an ester group in their N, but also with other functional groups in place of the ester, and more particularly the nitrile or amide functions.

 This improvement is due, in the first place, to the fact that the olefinic radical which is reacted with the imine is in the form of carbonate, the CO 3 group being bonded to the C atom in carbon of carrier carbon of the double bond. The invention is based on the quite unpredictable discovery that such an olefin carbonate reacts well with imines in the presence of catalysts, in a neutral medium, while an alkaline substance must be added when the olefinic radical is bound to another group, especially -OH or acyl, for example acetyl.

 Another improvement according to the invention lies in conducting the reaction at moderate temperatures, preferably between 0 and 500C and especially in the vicinity of room temperature.

 As in the prior art, the process according to the invention is carried out in the presence of a palladium or platinum compound, preferably complexed with a phosphorus derivative. An advantageous embodiment consists of employing a catalyst formed by the combination of a Pd atom with, as ligands, two moles of a phosphine, a 7-allyl group and a counter-ion which may be, for example, EtO, AcO r BF4 or other.

 Thus, the process according to the invention consists in reacting an imine, bearing an N-functional group, with an olefinic radical, in the presence of a Pd or Pt compound, within a solvent, and is characterized in that the olefinic radical is in the form of carbonate whose -CO3 group is bonded to the carbon atom of the olefin in the double bond.

The reaction of the process can be represented as follows

I- (imine) II- (olefinic compound)

<tb><SEP> R1 <SEP> R1
<tb> 3 <SEP> C = N-CR3-. <SEP> 3
<tb><SEP> Z <SEP> \ C = N-CR3-Z <SEP> or / and <SEP> C = N-CR <SEP> -z
<tb><SEP> R2 <SEP> CH-C = CH-R <SEP> R <SEP> R-CH-C = CH-R5
<tb><SEP>'5<SEP> 14 <SEP> R
<tb><SEP> R <SEP> R <SEP> 14
<tb><SEP> III <SEP> (alkenylated imine <SEP>) <SEP> III '
<Tb>
+ CO2 + R6OH ........................................ (1)
Each of the radicals R to R6, which may be the same or different, may be a hydrogen atom or a hydrocarbon group, in particular aliphatic, saturated or unsaturated, cycloaliphatic, aryl or alkaryl, which may carry substituents, for example halogens, nitriles, hydroxyls and acyls. , nitro, amide, sulphone, ester, or the like. More particularly, these radicals are C1-C18 alkyls, cycloalkyls, and the like.
C5 or C6, phenyls, alkylphenyls and naphthyls.

The most common groups R to R6 are alkyls in
C1 to C4, phenyl and benzyl.

Z denotes a functional group which may be for example ester, thioester, dithioester, sulphonyl, sulfinyl, nitrile, amide, thioamide or other. Thus Z can be of the type -CO2R7, -CSOR7, -CS2R7, -SO2R7, -SO3R7, -C # N, -CONH2,
PO3R7, -CSNH2 and C-R7 denoting a group which may be one of those referred to above with respect to R to R6; in most syntheses R7 is methyl or ethyl, when the Z group has to be transformed during the application of the imine produced.

 In the case where it is intended to hydrolyze the alkenyl imine to the corresponding amine, the above-mentioned Z groups make it possible to obtain an amine carrying a second, other function, for example amino-acid, amino-thioacid, amino-dithioacid, amino-sulfonate, amino-nitrile, aminoamide, or aminophosphonic peptide, etc.

 The olefinic radical carbonate employed according to the invention is preferably a double carbonate of the olefin and a lower alkyl R 6 leading to an alcohol R 6 OH, as shown by the reaction (1), easy to separate and recover.

By way of example, where R 1 is phenyl, R and R 2 to R 5 are H, R 6 is C 2 H 5 and Z is CN, reaction (1) becomes

It should be noted that the process of the invention makes it possible to obtain mono-alkenyl derivative exclusively, if one mole of each of the reagents is used, whereas the methods of the prior art generally lead to mixtures of imine mono- and di-allylated when both
H on the carbon in o (nitrogen are present, as in the reaction (2) above illustrated.

 The procedure of the process of the invention comprises the dissolution or dispersion of the starting imine in a liquid, in particular a solvent, which is chemically inert with respect to the compounds to be employed. Depending on the solubilities of these, the various known organic solvents can be used, such as benzene, toluene, chloroform, alkyl esters, dioxane, etc., in particular tetrahydrofuran and diethylformamide.

 The concentration of the reactants is generally from 1 mole of imine to alkenyl and 1 mole of carbonoinconfinic alcohol for 0.6 to 6 liters of solvent, and preferably for 2 to 4 liters; in other words, 0.16 to 1.6 moles of each of the reactants are used per liter of reaction medium, the preferred proportions being 0.25 to 0.5 mole.

 With regard to the catalyst, although very small proportions can be used, it is advisable to put in the reaction medium an amount corresponding to 0.01-0.1 Pd atom or / and Pt per mole d treated imine; the best proportions are from about 0.02 to 0.06 such atoms per mole of imine.

 The catalyst may be prepared in advance or well formed in situ during the alkenylation reaction.

 A mode of preparation, prior to the reaction itself, which gives a highly active catalyst, consists of dissolving a complex of Pd or Pt, such as palladium (dibenzylidene acetone) 2 or Pd (dba) 2 in a suitable solvent and to add to it, per metal atom, one mole of an olefinic radical compound combined with a d-functional group of carbon bearing the double bond; two moles of a ligand constituted by an organic phosphorus derivative, at 1 atom P each, or a mole of such a derivative having 2 P atoms connected by a hydrocarbon bridge, are then added to the solution. The solvent can then be evaporated and the complex formed in the solid state to be collected in order to introduce the appropriate amount into a reaction medium.

 It is convenient to employ, as the olefinic radical compound, for the formation of the catalyst, the same double carbonate of olefin and a recylated alkyl II of the reaction (1) given above which is to be used for the formation of the catalyst. alkenylation of imine. This can be, for example, propenyl carbonate and ethyl.

 Useful organo-phosphorus, trico-ordinated, symmetrical or asymmetric ligands are phosphines, phosphites, phosphonites, amino-phosphines, triaminophosphines, diphosphines, diphosphinites, diphosphonites and the like.

Excellent results have been obtained, as shown by the examples illustrating the invention, with the complexes of compositions

<tb> (a) <SEP> (b)
<tb><SEP> pa <SEP> (dba) 2
<tb> + <SEP> X <SEP> + <SEP> CH2 = CH-CEZ-OCOC, H
<tb><SEP> CH5 <SEP> p <SEP> P <SEP> / <SEP> sC6H5
<tb><SEP> + <SEP>;; P-CH2 <SEP> CH2 <SEP> -P
<tb><SEP> CH <SEP> CH
<tb><SEP> or <SEP> (c)
<tb><SEP> Pd-bis (diphenylphosphino) -1,2-ethane
<tb><SEP> to abbreviation <SEP> Pd (dppe) 27
<tb><SEP> + <SEP> CH2 = CH-CH2-OCO-C2H5
<tb><SEP> O
<Tb>
It is often advantageous for the yield of the alkenyl imine and the purity thereof to use cationic complexes, such as (a>, in which X is a BF4 or PF6
When one wants to form the catalyst within the solution or dispersion of the reagents, it suffices to add the commercial complex of Pd or Pt, such as the
Pd (dba) 2 and the ligand, in particular an organophosphorus product, to the reaction medium containing the imine and the olefinic compound.

 If a zero-valent complex such as Pd (dppe) 2 is used, it is no longer necessary to add an organophosphorus ligand to the medium.

 According to a particular feature of the invention, in order to obtain an isomer of the alkenyl imine, where the alkenyl is attached by its position 1 with respect to the double bond, a catalyst whose ligand is sterically hindered is used. This is particularly the case of the isomer III 'of the reaction (1) shown above.

 The process according to the invention can be carried out at various temperatures ranging between -800 and + 1000C whose choice depends on the reactivity of the bodies in the presence and the activity of the catalyst. In general, the temperatures of about 0.degree. C. to 500.degree. C. and, in particular, those of the environment, namely about 150 to 400.degree.

 Depending on the temperature and the nature of the reagents, the alkenylation according to the invention is carried out in 1 to 48 hours and most often in 1 to 8 hours.

 The invention is illustrated without limitation by the following examples.

EXAMPLE 1 Preparation of N- (chloro-4'-benzylidene) -ethyl-allXl ethyl glycinate

<tb> Cl-CH = N2CH-COOC25
<tb><SEP> CH <SEP> = CH2
<tb><SEP> CH
<tb><SEP> (Compound
<Tb>
This preparation is carried out according to the method of the prior art, for the purpose of comparison with the following examples, illustrating the process of the invention.

The general reaction (1), seen above, is carried out with, as imine I, p.chloro-phenyl imino ethyl acetate
Cl-C6H5-CH = N-CH2COOC2H5, and - as olefinic compound II - methyl-allyl acetate

1 ml of tetrahydrofuran (THF), suspended in 0.5 ml of purified NaH, is added to a 1-liter glass flask and 0.5 mol of the abovementioned imine I is added and the mixture is shaken. during 1 hour. 0.5 mole of olefinic compound II above and 0.025 mole of commercial bis (diphenylphosphino) -1,2-ethanepalladium are then added to this medium for the formation of the catalyst in situ.

The stirring is maintained for a further hour at 20 ° C., then 0.5 mol of water is added, which hydrolyses the NaH.The organic solvent phase (THF) is dried and then evaporated, the residue is taken up in 1 liter. of ether and filtered on celite.

Further evaporation gives a crude product which is chromatographed on silica.

A thick, light yellow oil is thus obtained, boiling at 1450 ° C. at 0.01 mm Hg. The yield of this product is 60% relative to the imine used.

Characterization in 1H NMR (CDCl3) gives
triplet 1.3 ppm (3H) quadruplet 4.1 ppm (2H)
singlet 1.7 "(3H) multiplet 4.3-4.6" (3H)
singlet 2.55 "(1H) doublet 7.3 ppm (2H)
singlet 2,65 "(1H) doublet 7.6 ppm (2H)
singlet 8.06 ppm (1H)
IR: (neat) vC = O 1710 cm 1
EXAMPLE 1 bis
The operations of Example 1 are repeated in the same way, but without the presence of NaH. Under these conditions, no reaction takes place, even after several hours of maintaining the reagents, with stirring, at 200C.

EXAMPLE 2 Preparation of ethyl N- (chloro-4'-benzylidene) -methyl-allyl glycinate (same compound VI as in Example 1) by the process of the invention.

The procedure is the same as in Example 1, but the methyl-allyl acetate (compound II) is replaced by the same number of moles of ethyl and methyl-allyl double carbonate.

(Compound V) and there is no NaH in the reaction medium.

The alkenylated imine (compound IV) is then obtained with a yield of 90%, and the NMR and IR characterizations show that this product is identical to that which results from Example 1.

Thus, because of the use of olefin carbonate instead of acetate, the yield was increased from 60 to 90%, while saving 1 mole of NaH per mole of treated imine.

EXAMPLE 3
Preparation of methyl propenyl N- (diphenyl methylene) glycinate

et du carbonate double de propényle et d'éthyle

molécule pour molécule, et 0,05 atome de Pd, sous la forme indiquée dans exemple 1, par mole d'imine.<tb><SEP> CH
<tb><SEP> C = N-CH-COOCH3
<tb><SEP> C6H5 <SEP> CH2-CH = CH <SEP> (compound <SEP> VI)
<tb> The <SEP><SEP> operating mode <SEP> is <SEP> the <SEP> same <SEP> than <SEP> the previous <SEP> example
<tb> but starting from methyl diphenyl-methylene-imino acetate

and double carbonate of propenyl and ethyl

molecule for molecule, and 0.05 Pd atom, in the form indicated in Example 1, per mole of imine.

The reaction time at 20 C is 2 hours. The product obtained is a white oil, indistillable. His examination in
H NMR (CDCl3) gives
2.65 multiplet (2H)
3.7 singlet (3H)
4.2 triplet (1H)
4.9-5.3 multiplet (2H)
5.5-6 multiplet (1H)
7.2-7.8 multiplet (10H)
IR: VC = O 1735 cm-
VC = C 1620 cm 1
Yield on the starting imine: 80%.

EXAMPLE 4
Preparation of cinnamyl N- (diphenylmethylene ethyl glucinate

(Compound VII) (Compound VIII)
The operations are the same as for Example 3, with the same starting imine, but the olefinic compound is the double carbonate of ethyl and cinnamyl.

The combination of the two isomers VII and VIII is obtained with a yield of 80%. The body content VIII is 5.2%.

Here are the characteristics NMR 1H (CDCl3) and IR of these new compounds, constituted by an indistillable white oil
VII VIII multiplet 2.82 ppm (2H) singlet 3.75 ppm (3H) singlet 3.75 ppm (3H) multiplet 4.12 ppm (1H) triplet 4 ppm (1H) triplet 4.25 ppm (1H) multiplet 6 5-5.8 ppm (2H) multiplet 5.12-5.45 ppm (2H) multiplet 6.95-7.75 ppm (15H) multiplet 6 -6.75 ppm (1H)
multiplet 7.15-8 ppm (15H)
IR: (pure) C = O 1730 cm 1 IR: (neat) C = O 1730 cm 1
C = C 1620 cm 1 C = C 1620 cm 1
EXAMPLE 5
Preparation of the same compound VII as in Example 4, but practically free of its isomer VIII.

The procedure is as in Example 4, but the catalyst is prepared in advance by combining 2 moles of chloromethallyl-PQ7 complex with 4 moles of bis (diphenylphosphino) 1,2 ethane and 4 moles BF4Ag in chloroform, stirred for 4 hours. hours in an inert atmosphere at room temperature.

As before, the catalyst is employed at 0.05 Pd atoms per mole of treated imine.

It is seen that the presence of a cationic complex of the type (a), described above, associated with negative X ions, here
BF4, makes it possible to obtain the isomer VII alone. A similar result is obtained with PF6 instead of BF4.

EXAMPLE 6
Preparation of methyl N- (diphenyl-methylene) -methyl propenyl glycinate.

optically active.

The operations are analogous to those of Examples 2 to 5, starting from diphenyl-methylene imino-methyl acetate (as in Example 3) and ethyl and methyl-propenyl double carbonate (compound V of the example 2), but the catalyst, prepared in situ, is formed by the action of 1 mole of complex Pd (dibenzylidene acetone) 2 on 2 moles of (-) chirophos,

With this catalyst, at a rate of 0.08 Pd atom per mole of imine, the desired product is obtained with a yield of 65%, characterized by a [&alpha;] D of -22.5 (c = 0). 76 / CHCl3), ie 13.2% ee.

EXAMPLE 7
Use of an olefinic carbonate bearing an acetyl group
According to the technique of Example 2, 1 mole of CH3 diphenyl methylene glycinate is reacted with 1 mole of ethyl and acetobutenyl double carbonate.

<Tb>

<SEP> A <SEP> B
<tb><SEP> CH3COO-CH2-CH = CH-CH = OCO-C2Hj
<tb><SEP> 5
<tb> After <SEP> 8 <SEP> hours <SEP> to <SEP> 200C, <SEP> then <SEP><SEP> seperation described <SEP> previously,
<tb> an indistillable white oil is obtained with a yield of 70% with the following NMR characteristics
singlet 2 ppm (3H)
multiplet 2.6 ppm (2H)
singlet 3.75 ppm (3H)
triplet 4.10 ppm (1H)
multiplet 4.42 ppm (2H)
multiplet 5.50 ppm (2H)
multiplet 6.95-7.75 ppm (1OH)
The product meets the formula

It is interesting to observe that it is the carbonate group (B) which reacted, while the aceto group (A) remained attached to the final molecule. The process according to the invention, with carbonates, thus makes it possible to fix on an imine an alkenyl carrying a carboxylic group.

EXAMPLE 8
Alkenylation of an imine carrying a nitrile function using a double carbonate of ethyl and alkenyl acetate.

avec 1 mole de même carbonate d'éthyle et d'acéto-butényle que dans l'exemple7, pendant 8h à 200C, en présence du même catalyseur formé in situ (comme dans l'exemple 1).The procedure is that of Example 7. One mole of cyanoimine is reacted.

with 1 mole of the same ethyl carbonate and of aceto-butenyl as in Example 7, for 8 hours at 200 ° C., in the presence of the same catalyst formed in situ (as in Example 1).

dont les caractéristiques sont
RMN 1H(CDCl3). The product obtained, with a yield of 80%, is cyano-5 (diphenyl-methylene-amino) -5-pentene-2-yl acetate.

whose characteristics are
1H NMR (CDCl3).

singlet 2.02 ppm (3H)
multiplet 2.67 ppm (2H)
triplet 4.3 ppm (1H)
multiplet 4.5 ppm (2H)
multiplet 5.75 ppm (2H)
multiplet 7.15-7.87 ppm (10H)
IR: (pure) C = O 1730 cm
C = N 2230
C = C 1610
It is in the form of a white oil, thick, indistillable.

désignés plus haut par II dans la réaction (1).EXAMPLES 9 to 11
Alkenylation of cyanoimine (C6H5) C = N-CH2CN with carbonates of various olefinic radicals, of general form

designated above by II in reaction (1).

dans le rapport de 4P à Pd, à raison de 0,015 atome Pd par mole d'imine initiale.The catalyst is formed in situ by the addition of bis (dibenzylidene acetone) -Pd and organophosphorus (-) chirophos,

in the ratio of 4 P to Pd, at a rate of 0.015 Pd atom per mole of initial imine.

The reaction is carried out at 20 ° C in an inert atmosphere with stirring for a time which is indicated in the table of results below.

Ex. NO R R4 R5 Duration R% Êi D
hours
9 HHH 26 90 -23.50
10 H CH3 H 72 50 -21.1
11 C6H5 HH 26 100
EXAMPLE 12
An operation similar to that of Examples 9-11 is carried out with a carbonate having R = H, R4 = H and R5 = CH3, the organophosphorus compound of the catalyst being replaced by (+) - 4,5-dimethylphenyl -2 trimethyl-1 ', 1', 2 'cyclopentylene -2', 5 '(2'R, 5'S) -4,5 dioxaphospholane-1,3,2 (2S, 4S, 5R), and the proportion of catalyst is 0.03 atom
Pd per mole of imine.

The operation lasts 10 hours and gives a yield of 70%; the enantiomeric excess is 7%.

pratiquement dans les mêmes conditions qu'à l'exemple 9. EXAMPLE 13 Alkenylation of amido-imine (C6H5) 2C = N-CH2-CO (C2H5) 2
Operating as in Example 9, but from this amido-imine we obtain the body

practically under the same conditions as in Example 9.

dans les mêmes conditions que pour l'exemple 2. EXAMPLE 14
Alenylation of thioesterimine Cl-C6H4-CH-N-CH2-CSO-C2H5 with double carbonate (composted V) according to Example 2
We obtain the product:

under the same conditions as for example 2.

Claims (15)

claims  1. Process for alkenylation of imines carrying a functional group in Zl of their nitrogen atom by the action, on such an imine, of an olefinic radical, in the presence of a Pd or Pt compound as catalyst , in a solvent, characterized in that the olefinic radical is in the form of a carbonate whose CO3 group is bonded to the C atom of the olefin at i of the double bond thereof.  2. Process according to claim 1, characterized in that one of the CO3 bonds is saturated with an alkyl, preferably C1 to C4.

<Tb>  <SEP> 3. <SEP> Process <SEP> next <SEP> the <SEP> claim <SEP> 1 <SEP> or <SEP> 2, <SEP> in <SEP> the <tb> which <SEP> the imine <SEP> is <SEP> R2C = N-CH-Z <SEP> where <SEP> each <SEP> of <SEP> symbols <SEP> R1, <SEP> R2 <tb> <SEP> R3 <tb> and R3 may designate an H atom or a hydrocarbon group and Z a functional group, characterized in that one or more of these hydrocarbon groups carry substituents, in particular halogen, nitrile, hydroxyl, acyl, nitro, amide, sulfone or ester.  4. Method according to one of claims 1 to 3, characterized in that said functional group (Z) is thioester, dithioester, sulfonyl, sulfinyl or phosphonyl.  5. Method according to one of claims 1 to 3, characterized in that said functional group (Z) is a nitrile, amide or thioamide.  6. Process according to one of the preceding claims, wherein the olefinic carbonate employed is of the form

 wherein each of R, R and R 5 denotes an H atom, a hydrocarbon group capable of carrying a substituent, characterized in that one or more of them are C 1 to C 18 alkyls, C 5 or C 6 cycloalkyls, phenyls, alkylphenyls and / or naphthyls.  7. Process according to the preamble of claim 6, characterized in that one of the symbols R, R4 and R5 comprises a carboxylic group.  8. Method according to one of the preceding claims, carried out in the presence of a complex of Pd or Pt, cationic, with an organo phosphorus compound as ligand, characterized in that a negative ion compound, in particular BF4 or PF is present in the reaction medium.  6  9. Method according to one of the preceding claims, characterized in that the reaction is carried out between 0 and 500C, in particular at room temperature.  10. Process according to one of the preceding claims, used for the preparation of an optically active imine, in the presence of a Pd or Pt complex, characterized in that a complex whose ligand is asymmetrical is employed.  11. A process according to one of the preceding claims for the preparation of an alkenyl imine in which the alkenyl is attached by its position 1, characterized in that a catalyst is employed in which the ligand is sterically hindered.  12. New imine, bearing a functional group on the C in i of its N iminic atom and an alkenyl group on the same carbon atom, of general formula

  where the radicals R to R5, which are similar or different, are H atoms or hydrocarbon groups which may carry substituents, characterized in that Z is a thioester, dithioester, sulphonyl, sulfinyl, phosphonyl, nitrile, amide or thioamide group.  13. A novel alkenyl imine according to the preamble of claim 12, Z being an ester group, characterized in that R has a carboxyl.  14. A novel imine according to the preamble of claim 12, Z being an ester group, characterized in that R is a phenyl.  15. New imine according to claim 12, characterized in that R is a phenyl or a group comprising a carboxyl.  16. Application of the process or the product according to one of claims 1 to 15, to the production of an amino acid, alkylated to N, by hydrolysis and hydrogenation of the corresponding alkenyl imine.