Stereoselectivity of electrophile-promoted oxacyclizations of 1,4-dihydroxy-5-alkenes to 3-hydroxytetrahydropyrans
摘要:
Stereoinduction from the allylic hydroxyl group of 1,4-dihydroxy-5-alkenes has been systematically explored with various alkene substitution patterns and electrophilic reagents. For formation of erythro-diastereomers of 2-substituted 3-hydroxytetrahydropyrans, mercuric trifluoroacetate-promoted cyclizations of cis- and (Z)-alkenyldiols generally give the highest diastereoselectivities. For the corresponding 1,4-dihydroxy-5-alkyne, mercuric triflate-catalyzed cyclization followed by triethylsilane reduction affords an alternative route to the euthro-diastereomer. (C) 2013 Elsevier Ltd. All rights reserved.
Total syntheses of the diterpenoids (−)-kolavenol and (−)-agelasine B
摘要:
The trans-clerodane diterpenoids (-)-kolavenol (2) and (-)-agelasine B (1) have been prepared from the enantiomerically pure decalone 3. The key steps of the syntheses involve the stereoselective alkylation of the nitrile 4 (to give 5), the efficient coupling of the iodides 10 and 11 to produce the clerodane skeleton 12, and the electrochemical reduction of 16 to provide (-)-1.