ASYMMETRIC PAUSON-KHAND REACTION - COBALT-MEDIATED CYCLOISOMERIZATIONOF 1,6-ENYNES IN CARBOHYDRATE TEMPLATES - SYNTHESIS OF BIS-HETEROANNULATED PYRANOSIDES

The Pauson-Khand reaction on the carbohydrate derived precursors 1-6 i s reported. We have described for the first time the cobalt-mediated c yclization of some O-branched chain 1,6-enynes in carbohydrate templat es. The resulting bis-heteroannulated pyranosides 17-22 have been obta ined in diastereomerically pure form, in moderate to good yield, and i n one, simple synthetic operation. These enantiomerically pure, densel y functionalized carbocycles are attractive advanced intermediates for the synthesis of complex natural products.