Fixation of heterocumulenes, II A study on the reaction of lithiated allylsystems with CO2, isocyanates and isothiocyanates

The regioselectivity of the reaction of 1-(thiophenyl)- (Li-6), 1-(phenylsu lfinyl)- (Li-12), 1-(phenylsulfonyl)- (Li-15) and 1-(diethoxyphosphoryl)all yllithium (Li-18) with CO2, PhNCO and PhNCS is investigated. Carboxylation of the allyl sulfide 6 and the allyl sulfoxide 12 proceeds with low regiose lectivity On the other hand, an exclusive gamma-selectivity is achieved for reactions of CO2 with Li-15 and Li-18. Both carboxylations are reversible and can be directed to give a-products by using low temperature workup (0 d egrees C). In contrast to CO2, PhNCO reacts with the allylic compounds inve stigated here to give amides with a high degree of regioselectivity: alpha- Attack is found for the sulfide 6 and the sulfone 15 whereas the reaction o ccurs at the gamma-terminus for the sulfoxide 12 and the phosphonate 18. Ex clusive alpha-attack is observed for all sulfur-substituted allyllithium co mpounds on reaction with PhNCS. In contrast to this, reaction of the phosph onate 18 with PhNCS yields exclusively the gamma-product.