Reversible crotylstannation of carbonyl compounds. Crotylstannation ability of Bu3-nClnSnCH2CHCHCH3 (n = 0, 1, 2) compounds towards acetone and benzaldehyde and 13C NMR characterization

The crotylstannation reaction: {A figure is presented} has been found to be reversible. The compounds trans/cis-Bu3-nCln SnCH2CH= CHCH3 (n = 0, 1, 2) have been prepared by elimination reactions of organostannoxy compounds,Bu3-nClnSn-O-C(Me)(i-Pr)CH(Me)CHCH2, which were synthesized by means of transalkoxylation between Bu3-nCInSn(OMe) compounds and threo/erithro-2,3,4-trimethyl-5-hexen-3-ol. Under the conditions used the elimination occurs stereospecifically and with complete allylic rearrangement. The ability of the organostannoxy compounds to yield crotyl butylchlorotins via elimination increases in the order, Bu3Sn-O-C < Bu2ClSn-O-C < BuCI2Sn-O-C. In the addition reactions, the sequence of increasing reactivity is Bu3SnCrot < CIBu2SnCrot < CI2BuSnCrot (Crot = crotyl). The 13C NMR spectra of the compounds made reveal that the chemical shifts of the allylic carbon atoms are related to the inductive effects of the chloro-substituents