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Paper | Special issue | Vol 52, No. 1, 2000, pp.171-183
Published online, 1st January, 1970
DOI: 10.3987/COM-99-S4
Oxetane Formation by 1,3-Migration of Benzyloxy Group in 7-Oxabicyclo[2.2.1]hept-2-yl Cations: Synthesis of 4,7-Dioxatricyclo[3.2.1.03,6]octane and 2-Oxabicyclo[2.2.2]octane Encrusted in the 1,4:5,8-Diepoxy-perhydrophenanthrene Ring System

Hervé Mosimann and Pierre Vogel*

*Section de Chimie de l’Université, BCH, CH-1015-Lausanne-Dorigny, Switzerland

Abstract

Epoxidation of (1RS,2SR,3SR,4RS,6RS,7RS,8RS,12RS,13RS)-6,13-bis(benzyloxy)-15, 16-dioxapentacyclo[10.2.1.14.7.02,11.03.8]hexadec-10-en-8-yl-methanol (12) led to the stereoselective formation of (1RS,2RS,3RS,5RS,6SR,7RS,8RS,10RS,11SR,12SR,16SR)-3,10-bis(benzyloxy)-13,17,18-trioxahexacyclo[10.2.2.12,5.18,11.01.6.07.12]octadecan-16-ol (13). Epoxidation of the acetate (19) derived from 12 gave an epoxide (20) that generated (1RS,2SR,3RS,4RS,6RS,7SR,8RS,9SR,11RS,12RS,13RS)-13-benzyloxy-9-hydroxy-15,16,17-trioxahexacyclo[10.2.1.14,7.16,8.02,11.03,8]heptadecane-11-methyl acetate (21) under acidic conditions. These reactions imply the formation of 2-alkyl-6-endo-benzyloxy-7-oxabicyclo[2.2.1]hept-2-yl cation intermediates (e.g. 14) that are quenched intramolecularly by the hydroxymethyl group to give the corresponding 2-oxabicyclo[2.2.2]octane systems (1213). In the case of the acetoxymethyl containing intermediate, the latter cyclization is retarted and a facile 1,3-migration of the endo-benzyloxy group occurs leading to the corresponding 4,7-dioxatri-cyclo[3.2.1.03,6]octane derivative (2021).