Molecular and Crystal Structure of Two Anthracene Derivatives and their 1,4-Endoperoxides. Influence of the Aromatic Ring Distortion upon the Steric Acceleration of the 1,4-Addition of Singlet Oxygen

Abstract

The X-ray structure determination of two anthracene derivatives, namely 1,2,3,4-tetramethylanthracene (TMA) and 1,2,3,4-tetramethyl-9,10-diphenylanthracene (TMDPA), and of their endoperoxides, 1,2,3,4- tetramethyl-1,4-dihydro-1,4-epidioxyanthracene (TMAPO) and 1,2,3,4-tetramethyl-9,10-diphenyl-1,4-dihy- dro-1,4-epidioxyanthracene (TMDPAPO), has been performed. The compared analysis of the conformations of the four molecular structures strongly suggests that the steric acceleration observed for singlet oxygen addition to TMDPA should be attributed to the important distortion of the anthracene nucleus.