We performed diastereodifferentiating [2+2] photocycloaddition of chiral cyclohexenone (1) with cyclopentene using a special continuous microflow reactor equipped with UV-LED lamps for photoreaction, and compared the results to batch processing. Even at very high sample concentration, the high conversion was accomplished in this microreactor: however, the reaction under the same conditions did not proceed to completion in the batch. Furthermore, the highest diastereomeric excess (de) of photoproducts was achieved in this microreactor when aromatic compounds were added, which prevented the reaction from proceeding to completion in the batch due to their high absorption coefficients. This diastereoselective enhancement was due to superior light penetration in the microreactor. (C) 2012 Elsevier B.V. All rights reserved.
Novel Enhancement of Diastereoselectivity of [2 + 2] Photocycloaddition of Chiral Cyclohexenones to Ethylene by Adding Naphthalenes
The additive effect on the diastereoselective [2 + 2] photocycloaddition of chiral cyclohexenones 1 to ethylene is examined. A novel and fairly efficient method of increasing the diastereoselectivity in the reaction of 1a was elucidated. The de value increased from 56% to 83% by the addition of 1-phenylnaphthalene. The major product 2a was isolated by the recrystallization of the diastereomeric mixture