7-Alkoxy allylic stannanes synthesis

Marshall, J A, Seletsky, B M, Luke, G P, Synthesis of protected carbohydrate derivatives through homologation of threose and erythrose derivatives with chiral y-alkoxy allylic stannanes, J. Org. Chem., 59, 3413-3420, 1994. 

In a demonstration of the synthetic utility of chiral y-alkoxy stannane reagents, Marshall and co-workers applied this methodology to the synthesis of the gypsy moth pheromones (+)- and (-)-disparlure [287]. The synthesis required the production of the [y-(alkoxy)allyl]stannane reagent 440 (Scheme 11-32). 

Optically active allyl stannanes thus obtained were treated with a-alkoxy aldehydes to give useful substrates for the synthesis of carbohydrates13. 

The presence of an a-alkoxy substituent on the substrate aldehyde leads to the formation of a differentially protected 1,2,3-triol upon addition of a y-oxygenated allylic stannane (Eq. 43). Such additions are of potential use for the synthesis of carbohydrates and extended polyols. The resident double bond in the adduct can be further functionalized by dihydroxylation or epoxidation to extend the polyol chain. 

A number of investigations have explored the reactions of ally lie stannanes containing a y-alkoxy substituent. A direct preparation of these substances utilizes the kinetic deprotonation of an allyl ether followed by alkylation with tri-n-butylstannyl chloride. In a typical experiment, the deprotonation of 101 with 5-butyllithium leads to internal coordination of lithium cation and provides formation of the Z-allylstannane 102. The behavior of y-alkoxyallylstannanes is similar to the corresponding Z-alkylstannanes, and as a result, the reaction provides a stereoselective route for the synthesis of complex diol derivatives. In the allylation of chiral aldehyde 80 with stannane 102, /l-chelation dictates face selectivity. The expected. yyn, anti-product 104 is obtained with high diastereoselection via the antiperi-planar 103, which accommodates the sterically demanding silyl (TBS) ether (Scheme 5.2.23).23... 

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