Synthesis of carbonyl compounds via tin-free radical carbonylation

Abstract

Free radical carbonylation has proved to be synthetically very useful for the synthesis of various carbonyl compounds. Most of previously developed synthetic methods based on free radical carbonylation require the use of organotin reagents as radical mediators, which are highly toxic and difficult to remove from the reaction mixture. To solve the problems associated with toxic organotin reagents, we have previously reported that alkyl allyl sulfone precursors are one of the most useful and reliable methods for the generation of alkyl radicals under tin-free conditions and are very effective in radical carbon-carbon bond formations. In connection with our continued efforts to achieve tin-free radical carbon-carbon bond formations, we studied tin-free radical carbonylation using alkyl allyl sulfone precursors to prepare various carbonyl compounds. Reaction of alkyl allyl sulfones as a radical precursor, carbon monoxide and various phenylsulfonyl derivatives as a radical trapping agent (S-phenyl benzenethiosulfonate, and phenylsulfonyl oxime ether) gives a corresponding carbonyl derivatives (thiol ester, and acylated oxime ether) in high yields under the optimized conditions (0.01-0.03 M heptane, 30-95 atm CO). In advanced studies, the direct conversion of aliphatic sulfonyl derivatives into the corresponding carbonyl derivatives based on tin-free radical carbonylation was investigated in which a new radical substrate was utilized not only as a radical precursor but also as a radical acceptor. 1Among the alkyl sulfonyl derivatives based on the thermal desulfonylation, alkyl thiosulfonates, alkyl sulfonyl cyanides, and alkyl sulfonyl oxime ethers were the most appropriate for new radical substrates, were directly converted into alkyl thioates, acyl cyanides, and acylated oxime ethers in high yields under pressured CO condition.