Asymmetric Pauson−Khand Reaction. Cobalt-Mediated Cycloisomerization of 1,6-Enynes in Carbohydrate Templates: Synthesis of Bis-Heteroannulated Pyranosides

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Abstract
The Pauson−Khand reaction on the carbohydrate derived precursors 1−6 is reported. We have described for the first time the cobalt-mediated cyclization of some O-branched chain 1,6-enynes in carbohydrate templates. The resulting bis-heteroannulated pyranosides 17−22 have been obtained in diastereomerically pure form, in moderate to good yield, and in one, simple synthetic operation. These enantiomerically pure, densely functionalized carbocycles are attractive advanced intermediates for the synthesis of complex natural products.