Journal
ANGEWANDTE CHEMIE-INTERNATIONAL EDITION
Volume 54, Issue 51, Pages 15497-15500Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/anie.201508405
Keywords
aminothiourea; cascade reactions; natural products; organocatalysis; spiroketals
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Funding
- Japanese Ministry of Education, Culture, Sports, Science and Technology
- Japan Society for the Promotion of Science for Young Scientists
- Grants-in-Aid for Scientific Research [15H05845, 15J06653] Funding Source: KAKEN
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Chiral spiroketal skeletons are found as core structures in a range of bioactive compounds. These natural compounds and their analogues have attracted much attention in the field of drug discovery. However, methods for their enantioselective construction are limited, and easily available optically active spiroketals are rare. We demonstrate a novel catalytic asymmetric synthesis of spiroketal compounds that proceeds through an intramolecular hemiacetalization/oxy-Michael addition cascade mediated by a bifunctional aminothiourea catalyst. This results in spiroketal structures through the relay formation of contiguous oxacycles, in which multi-point recognition by the catalyst through hydrogen bonding imparts high enantioselectivity. This method offers facile access to spiroketal frameworks bearing an alkyl group at the 2-position, which are prevalent in insect pheromones. Optically active (2S,5S)-chalcogran, a pheromone of the six-spined spruce bark beetle, and an azide derivative could be readily synthesized from the bicyclic reaction product.
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