Bromination of α-tocopherol methano-dimer and ethano-dimer

Bromination of the ethano-dimer of alpha-tocopherol (6) afforded pyrano-spirodimer of alpha-tocopherol (7) quantitatively, while the methano-dimer of alpha-tocopherol (10) produced a mixture of products, including the furano-spirodimer 11, pyrano-spirodimer 7, and 5-bromo-gamma-tocopherol (12), the latter two formed in ail unusual dealkylative fragmentation step. The mechanisms were studied by a combination of trapping reactions as well as kinetic and computational studies. (c) 2005 Elsevier Ltd. All rights reserved.