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The application of a tandem deconjugative aldol-cyclization sequence for the construction of substituted tetrahydrofurans was examined. The aldol condensation of alkenoates proceeded with alkylation at the -position to generate homoallylic alcohol moieties. These compounds could be induced to cyclize under the influence of iodine via an endo mode. The stereoselectivity for the cyclization occurred in good to excellent fashion. X-ray crystal structure analysis of three of the tetrahydrofurans established unambiguously the product stereochemistry. This was used to propose a transition structure for the cyclization which correctly predicts the observed product stereochemistry. By this method, virtually all the possible stereoisomers for the substituted tetrahydrofurans can be constructed by judicious choice of aldol product and/or olefin geometry.

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We have modified the substrate used in deconjugative aldol-cyclizations by incorporating the Evans chiral auxiliary. The deconjugative aldol step, using boron enolates, gave the expected products with complete syn-aldol stereochemistry. These compounds could then undergo an iodine-mediated cyclization to form optically active products. Oxetanes and fused ring tetrahydrofurans were easily assembled with a variety of substitution patterns and with excellent enantiocontrol. The deconjugation of acyclic chiral enimides resulted in the loss of control of olefin geometry. However, these compounds did appear to cyclize with excellent enantiocontrol.

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