Recent results in the free radical mediated synthesis of enantiomerically pure, highly functionalized carbocycles from carbohydrates

Abstract

The free radical cyclization strategy applied to precursors 1, 2 and 14 shows the power and the state of art of this ring closing method for the stereocontrolled synthesis of enantiomerically pure, highly functionalized carbocycles from carbohydrates. The tributyltin hydride mediated free radical cyclization of alkyne tethered N,N-diphenylhydrazones (1) and oxime ethers (2) give the stannylated aminocyclopentitol derivatives 4 and 11, respectively, in moderate yield and with complete stereoselectivity. The 6-exo-trig cyclization of aldehyde/oxime ether 14 derived from D-glucose has been revisited using tributyltin hydride as a reagent. This new protocol shows a superior stereoselection compared with the previous results obtained with samarium diiodide. In summary, an efficient protocol has been set up for the synthesis of enantiomerically pure, polyhydroxy aminocyclohexane derivatives, which are difficult to obtain by other methodologies.