SYNTHESIS OF CHIRAL ALPHA,DELTA-DIOXYGENATED ALLYLIC STANNANES AS REAGENTS FOR CARBOHYDRATE SYNTHESIS AND HOMOLOGATION

The delta-oxygenated allylic stannanes 4.4 and 4.5, prepared through a ddition of Bu(3)SnLi to gamma-OTBS crotonaldehyde 4.3c followed by eth erification of the adduct with TBS-Cl or MOM-Cl, undergo transmetalati on with InCl3 and in situ addition to aldehydes leading to mainly anti adducts 5.1 or 5.2, accompanied by varying amounts of syn diastereome rs. Selectivities of >95:5 can be realized with the MOM reagent 4.5 an d ynals 4.3d and 4.3e or cyclohexanecarboxaldehyde 4.3a. With enals 4. 3b and 4.3c, 80:20 mixtures of anti and syn adducts are formed. The S enantiomer 10.1 of stannane 4.5 has also been prepared as a reagent fo r carbohydrate synthesis. Accordingly, addition to alpha-ODPS acetalde hyde 10.2 in the presence of InCl3 leads to the adduct 10.3 as an inse parable 90:10 mixture of anti and syn diastereomers. Dihydroxylation o f the OTBS derivative 10.4 affords the potential altrose precursor 10. 5 in 81% yield.