Gold(I)-catalysed [3+3] cycloaddition of propargyl acetals and nitrones

In our series of investigations to expand the understanding of the gold(I) catalysis chemistry of propargyl acetals, a gold(I) catalysed [3+3] cycloaddition reaction of propargyl acetals with nitrones has been studied. A series of 5-methoxy-3,6-dihydro-2H-1,2-oxazine products with two stereogenic centres were obtained in a cis-stereoselective manner. The formal [3+3] cycloaddition reaction is supposed to go through O-nucleophilic attack of the nitrone on the C1 position of the gold complex generated from propargyl acetal followed by a final ring closure. An alternative C3 oxidation by nitrone affords aldehyde products and represents a competing pathway. The chemoselectivity of the cycloaddition reaction is discussed in order to demonstrate the potential and limitations of the reaction.

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