A new synthesis of endo-3,3-diphenyltricylco[3.2.1.0(2,4)]oct-5-ene and relative reaction rate study.

摘要

The new method for the preparation of endo-3,3-diphenyltricyclo[3.2.1.0 2,4]oct-6-ene (1), was developed. Although a synthesis had been reported earlier, the new approach affords a dramatic improvement in yield, reaction time and ease of operation. The major limitations of the old synthesis were the high cost of starting material, long reaction times, and multiple reaction products that had to be separated by difficult chromatographic methods. In this new synthesis, the starting materials are very affordable, accessible and easy to handle; the reaction times are short; and the side products are minimal. Exo-3,3-diphenyltricyclo[3.2.1.0 2,4]oct-6-ene (2) is easily prepared as reported by Wilt and Sullivan.;Endo-1 has a rigid geometry with an aromatic ring that is directly below and almost parallel to the plane containing the double bond. The aryl ring is, therefore, well positioned for aryl-pi participation during ionic additions to the double bond. Now organic chemists can more easily apply the relative reactivity ratios of exo-2 and endo-1 to the mechanisms of electrophilic additions. Previous applications of this technique were inhibited by the difficulty of preparing endo-1.;The relative reactivity study of oxidations on the two alkenes was related to the results of an earlier study of epoxidation with MCPBA which showed that the endo isomer reacted faster with k2/k1 = 0.72. The oxidations studied had similar reactivity ratios with the endo -1 reacting faster, which suggests development of charge in the transition states of these reactions.