Pressure Effect on the Product Distribution in Competing Reactions: Formation of a Bis Diels-Alder Adduct Via an Aromatizable Intermediate

摘要

The endo mono-adduct of cyclopentadiene with methyl p-benzoquinone does not react with excess diene even if it is well purified (if it is not, aromatization intervenes). However, at pressures of 700-800 MPa (7-8 kbar), the second cycloaddition step overtakes this reaction, and two bis-adducts are formed in a 4:1 ratio. Their configurations were determined by means of X-ray diffraction of derivatives to be endo, anti, endo and endo, anti, exo, respectively. A semicarbazone derivative of the main bis-adduct also could be prepared at high pressure only. The observations again demonstrate the usefulness of high pressure even in routine synthetic transformations. Keywords: High pressure reactions; Diels Alder reaction; Cyclopentadiene; X ray structures; Cyclic compounds; Pentadienes; Reprints. (MJM)