α,β-Unsaturated Acetals as Precursors of α-Substituted Ethoxy Dienes. Useful Reagents for Nucleophilic Acylation

Article abstract of DOI:10.1021/jo00097a059

The reaction of (E)-1,1-diethoxybut-2-ene (1a) and 1,1-diethoxy-3-methylbut-2-ene (1b) with 2 equiv of sec-butyllithium complexed with potassium tert-butoxide (Schlosser's base) in THF at -95 deg C gives 1-metalated 1-ethoxy 1,3-dienes that are synthetically equivalent to acyl anions.Subsequent reaction with suitable electrophiles, such as alkyl halides, aldehydes, ketones, carbon dioxide, and carboxylic acid derivatives, affords (E)-1-substituted 1-ethoxy 1,3-dienes 2a-i.Experimental procedures are given for the reaction of the carbanionic intermediates with the electrophiles.Some typical examples for the conversion of the produced α-substituted alkoxy dienes into the corresponding α,β-unsaturated carbonyl compounds are also reported.In particular, in the case in which crotonaldehyde is used as an electrophile, the addition product 2c undergoes acid-catalyzed conversion to compounds 4c, 5c, and 6c as a function of the experimental conditions.