Carbocyclization of carbohydrates: diastereoselective synthesis of (+)-gabosine F, (-)-gabosine O, and (+)-4-epi-gabosine O.

Exploitation of silica gel/chloramine T mediated intramolecular nitrile oxide-alkene cycloaddition (INOC) of sugar-derived oximes to carbocycles furnished the first synthesis of gabosine F from l-arabinose in 12 steps with 23% overall yield, thereby confirming its absolute configuration. Similarly, efficient syntheses of gabosine O and 4-epi-gabosine O were accomplished from D-mannose in 9 and 11 steps with 41% and 38% overall yields, respectively, involving INOC, regioselective dehydration, and diastereoselective hydrogenation as the key steps.