Aldehyde-alkene => allyl thioethers

Mixed bimetallic reagents possess two carbon-metal bonds of different reactivity, and a selective and sequential reaction with two different electrophiles should be possible. Thus, the treatment of the l,l-bimetailic compound 15 with iodine, at — 78"C, affords an intermediate zinc carbenoid 16 that, after hydrolysis, furnishes an unsaturated alkyl iodide in 61% yield [Eq. (15) 8]. The reverse addition sequence [AcOH (1 equiv), —80 to — 40 C iodine (1 equiv)] leads to the desired product, with equally high yield [8]. A range of electrophile couples can be added, and the stannylation of 15 is an especially efficient process [Eq. (16) 8]. A smooth oxidation of the bimetallic functionality by using methyl disulfide, followed by an acidic hydrolysis, produces the aldehyde 17 (53%), whereas the treatment with methyl disulfide, followed by the addition of allyl bromide, furnishes a dienic thioether in 76% yield [Eq. (17) 8]. The addition of allylzinc bromide to 1-octenyllithium produces the lithium-zinc bimetallic reagent 18, which can be treated with an excess of methyl iodide, leading to only the monomethylated product 19. The carbon zinc bond is unreactive toward methyl iodide and, after hydrolysis, the alkene 19... 

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