Addition of Organometallic Compounds to Tin-Containing Cyclic Ketones. Remote Stereocontrol Induced by the Stannyl Group

The addition of organometallic reagents to cyclic ketones bearing stannyl groups at an appropriate
distance to the carbonyl group occurs with a high level of stereocontrol, giving alcohols resulting from
attack of the nucleophile syn to the tin center. This remarkable remote control is a consequence of the
anchoring of the organometallic reagent by the tin and carbonyl groups. The degree of selectivity observed
depends on the spatial distance between the carbonyl group and the tin center. (Z)-β-Stannylvinyl ketones
(Sn/CO separation:  5 bonds) react with organolithium reagents, showing a high degree of stereocontrol.
On the contrary, the analogous ketones with E stereochemistry do not show selectivity at all. In the case
of β-stannyl ketones (Sn/CO separation:  3 bonds), the long distance between the tin center and the carbonyl
group does not favor selective addition except when allyllithium derivatives are used. A chelation-controlled
pathway assisted by the three-carbon chain of the allyl anion, which compensates the distance between
tin and carbonyl groups, has been proposed. The selectivity found for ketones 34−36 (Sn/CO separation: 
4 bonds) depends on their structure and varies with the hybridization of the carbon atom linked to the
trialkyltin group. Deuterium labeling experiments as well as ab initio molecular-orbital analysis support the
mechanistic hypothesis of an intramolecular delivery. Grignard reagents are less selective than organolithium
compounds.