ALPHA,BETA-UNSATURATED ACETALS AS PRECURSORS OF ALPHA-SUBSTITUTED ETHOXY DIENES - USEFUL REAGENTS FOR NUCLEOPHILIC ACYLATION

The reaction of (E)-1,1-diethoxybut-2-ene (1a) and 1,1-diethoxy-3-meth ylbut-2-ene (1b) with 2 equiv of sec-butyllithium complexed with potas sium tert-butoxide (Schlosser's base) in THF at -95 degrees C gives 1- metalated 1-ethoxy 1,3-dienes that are synthetically equivalent to acy l anions. Subsequent reaction with suitable electrophiles, such as alk yl halides, aldehydes, ketones, carbon dioxide, and carboxylic acid de rivatives, affords (E)-1-substituted 1-ethoxy 1,3-dienes 2a-i. Experim ental procedures are given for the reaction of the carbanionic interme diates with the electrophiles. Some typical examples for the conversio n of the produced alpha-substituted alkoxy dienes into the correspondi ng alpha,beta-unsaturated carbonyl compounds are also reported. In par ticular, in the case in which crotonaldehyde is used as an electrophil e, the addition product 2c undergoes acid-catalyzed conversion to comp ounds 4c, 5c, and 6c as a function of the experimental conditions.