The addition of an organostannane to carbonyl group is one of the most common and efficient methods for the production of contiguous, oxygen-containing stereocenters in organic molecules.
Since many naturally-occurring polymers contain this stereochemical motif, such as polypropionate and polyacetate, organostannane additon has been studied extensively by natural products chemists as a synthetically and comercially-important reaction.
(1)However, stoichiometrically relative amounts of metal-containing byproducts are generated by this reaction, and addition to sterically-encumbered pi-bonds in ketones, are uncommon.
Addition takes place via an SE' mechanism involving concerted dissociation of tin and C-C bond formation at the γ position.
With the allylstannane and aldehyde in high-temperature conditions, addition proceeds through a six-membered, cyclic transition state, with the tin center serving as an organizing element.
(6)The possibility of incorporating oxygen-containing substituents into allyl- and allenylstannanes expands their scope and utility substantially over methods relying on more reactive organometallics.
These compounds are usually prepared by enantioselective reduction with a chiral reducing agent such as BINAL-H.[9] In the presence of a Lewis acid, isomerization of α-alkoxy allylstannanes to the corresponding γ-alkoxy isomers takes place.
This step was carried out en route to (±)-patulolide C.[16] (11)Repeated use of the allylic stannane addition in an intramolecular sense was used in the synthesis of hemibrevetoxin B (one example is shown below).