Oxaallylic anions

Hoppe has investigated the regioselectivity of the reaction of oxaallylic anions generated from the N,N-diisopropyl carbamates of a variety of allylic alcohols. With carbonyl compounds reaction was found to take place predominantly at the y-carbon. The directing influence of the carbamoyloxy group was unfortunately diminished in alkylation reactions. 

The anions generated from the adducts of a, 3-unsaturated aldehydes and (8) are alkylated exclusively at the y-position. Evans et al. have also reported the alkylation of similar oxaallylic anions and the alkylation chemistry of diethyl (2-trimethylsilyl)ethoxymethylphosphonate has been reported. ... 

An example of an oxaallylic carbanion has been described by Oppolzer et alP In the alkylation of 3-triethylsilyloxypentadienyllithium (5 X = H) the y-alkylated product predominated. With the anion (5 X = SMe) alkylation occurs exclusively at the y-carbon atom. The synthetic potential of the anions (5) was demonstrated by the synthesis of bicyclic compounds via intramolecular Diels-Alder reactions of the alkylation products (Scheme 5). 

The enolates (48) and (49) of the transition metals tungsten, rhenium and molybdenum can be successfully prepared by the nucleophilic displacement of a-chloro ketones and a-chloro esters with the appropriate transition metal anion (Scheme 6). They are isolated as C-bound enolate derivatives and, except for the rhenium enolate (49), do not undergo thermal aldol additions to benzaldehyde. However, Bergman and Heathcock et al. have found that an aldol reaction of complex (48) with benzaldehyde can occur on irradiation via the rearranged q -oxaallyl derivative (50), where the metal aldolate (51) can then be... 

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