Tiglaldehyde aldimine, anion

Functionalization of tiglaldehyde. Anions of a,/5-unsaturated aldimines are known to react with electrophiles at both the a- and y-position. Thus, the lithium salt (1) of tiglaldehyde cyclohexylimine reacts with aldehydes to give, after acid hydrolysis of the imine, mainly the product of a-substitution. Addition of HMPT (1 equiv.) to the reaction followed by equilibration at 0° (2 hours) results mainly in formation of the product of y-subsitution. 

Anions derived from the aldimine of tiglaldehyde (14) react with carbonyl compounds preferentially at the a-position under conditions of kinetic control to give adducts (15), but products (16) derived from 7-attack are obtained under equilibrating conditions (Scheme 4). Addition of HMPA to the reaction or adduct mixture is required to promote isomerization of the initially formed a-adduct to the 7-product. There is also an increasing preference for 7-capture of the unsaturated imine anion as the degree of substitution a to the carbonyl function increases as in a-branched aldehydes and ketones (Table 2). Efforts to isomerize the initial a-adduct formed from reaction of the aldimine derived from crotonaldehyde with cyclohexanecarbaldehyde gave complicated mixtures. 

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