Free Radical Cycloisomerization of Enantiomerically Pure Alkyne- Tethered Oxime Ethers: A New Method for the Asymmetric Synthesis of Aminocyclopentitols.

Abstract We describe for the first time the free radical cyclization of enantiomerically pure alkyne-tethered oxime ethers obtained from carbohydrates. The synthesis of compounds 6 and 7 , obtained from 2,3- O -isopropylidene-D-ribose 3 is reported. These radical precursors have been submitted to cyclization with tributyl or triphenyltin hydride plus triethylborane, to yield, after ring closure, the aminocyclopentitols 8–10 . These carbocycles have been obtained as mixtures of Z and E vinyltin isomers, but with excellent diastereoselection. After protodestannylation only one diastereoisomer was detected. The absolute configuration at the new stereocenter formed during the ring closure has been established by detailed 1 H NMR analysis. The specific transformation of compound 9 (or 10 ) into aminocyclitol 14 is described. From these results, we can conclude that a new method for the asymmetric synthesis of aminocyclopentitols of biological interest is now available.