Propionaldehyde homoenolates

The concept of homoenolization was recognized by Nickon in the 1960s but attempts at direct formation of homoenolates were frustrated by cyclopropanolate formation. This lack of success has prompted the development of homoenolate equivalents19 of which the first example, the 3-propionaldehyde anion equivalent (112), was previously discussed (Sections 1.2.2.1.2 and 1.2.2.1.3). Ghosez has shown that a-cyanoenamines (249 and 250) add preferentially in the 1,4(7)-mode to cycloalkenones. The versatility of (250) which serves as either a (3-carboxyvinyl anion equivalent [-CH=CHCChR] or 3-propionate anion equivalent ["Cl ClfcCChR] (Scheme 85) is notable.191... 

Yet another development which is worth mentioning in this context is the 5n substitution of acetals of unsaturated carbonyl compounds. The phenomenon that the reaction of an allylic acetal with a Grignard reagent in the presence of CuBr may occur as a vinylogous substitution with double bond shift has been long known.The reaction can be utilized in an efficient synthesis of 3-substituted propionaldehydes using the acrolein acetal as a homoenolate cation equivalent (Scheme 38). ... 

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