Enamines methoxylation

A Once the 1,2-dihydroisoquinoline is formed by a Potneranz-Friisch synthesis between the reduced imine, from 4-methoxybenzaldehyde and ami noacetaldehyde diethyl acetal, it is combined directly with the l-(2-bromoethyl)-3-meihoxybenzene in a tandem two-steps-in-one procedure (Scheme 3.21), First the compound acts as an enamine and combines with the alkyl bromide at C-4, and then the methoxylated phenyl ring of the intermediate reacts with the iminium unit at C-3 to form the letracycle. 

The anodic oxidation of methyl N,/V-dialkylcarbamate in methanol, containing Et4NOTs, yielded three types of products a-methoxylated compounds, enamine-type products, and dealkylated carbamates.197 Methyl N-pyrrolidinylcarbamate (137), for example, gave on constant current oxidation... 

Tetrahydroquinoline derivatives can be obtained by cycloaddition of aromatic imines or immonium salts with enamines having an a-hydrogen186,187. Anodic oxidation of A,A-dimethylaniline 323 in methanol to a-methoxylated compound 324 and subsequent... 

These regiospecific photocyclizations to the root of the o-methoxyl group can be explained in terms of a nucleophilic attack from the enamine portion to the somewhat electron-deficient position at the root of the methoxyl group, as in the case of nucleophilic aromatic photosubstitution (33), and followed by a 1,5-sigmatropic shift of the substituent and its elimination to afford the didehydrolactam (1) as the final product (Scheme 5). 

The anodic oxidation of enamines in methanol containing sodium methoxide as the supporting electrolyte shows a reaction pattern different from that of enol ethers or enol acetates. The main products are mixtures of isomeric methoxylated enamines, (18) and (19), with yields in the range 74-76% (equation... 

TV.7V-Dimethylbenzylamine [64,65], 2,4.6-tris(dialkylamino)-l,3,5-triazines [66], N-(2,2,2-trifluoroethyl)amines [67,68], and TV-(2,2-difluoroethyl)amines [68] exhibit similar behavior. Methoxylation of enamines results in substitution at both the vinylic and the allylic positions [61]. 

In a study of the reduction of steroidal imines with lithium aluminium hydride and sodium borohydride, Lusinchi9 found that with an excess of lithium aluminium hydride the methoxylated imine (8) afforded the two isomeric imines, (12) and (13), together with N-demethylconanine (14), in a ratio dependent on the time of the reaction. The absence of iV-demethylheteroconanine indicated that the reduction at position 20 was stereospecific. The imine (12) was found to result from initial reduction of the 20-N-imine, while the imine (13) was suggested to be derived from an enamine derivative, as in Scheme 1. 

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