Synthesis, Structure, and Double Olefin Extrusion of All Three Diastereomers of 2,2,6,6‐Tetrakis(4‐chlorophenyl)‐3,7‐dimethyl‐4‐phenyl‐1,5‐dioxa‐4λ⁵‐phosphaspiro[3.3]heptane

A distorted tetragonal-pyramidal structure is adopted by the trans-trans diastereomer of the spirophos-phorane 1. In contrast, the cis-trans isomer displays a distorted trigonal-bipyramidal structure. These two as well as the cis-cis diastereomer were synthesized as stable crystals by taking advantage of electronic and steric effects of the methyl groups in the 3- and 7-positions. Interestingly, thermolysis of 1 gave two molar equivalents of Ar2CCHMe. Ar = 4-ClC6H4.