Synthesis and rigid conformers of 14,15-dimethyl-2,11-dithia[3.3](1,3)(1,4)cyclophane and 12,13-dimethyl[2.2](1,3)(1,4)cyclophane

Abstract

The dithiacyclophane 4 was synthesized from 2,3-dimethylaniline in seven steps. Only the con-former 4b was isolated. Photodesulfurization of 4b however resulted only in the isolation of the cyclophane 2a indicating an abrupt change in conformational preference going from the [3.3]phane to the [2.2]phane. Their stereochemistry could be assigned readily from the chemical shifts of the aryl protons or methyl protons on the (1,4)-bridged ring. Dynamic ¹H NMR studies indicated that both 2a and 4b remained conformationally fixed up to 150 °C. The conformational preference depends on the non-bonding interaction between H8 (of 2a) or H9 (of 4a) and the methyl groups and that between the (1,3)-bridged ring and the methyl groups in 2b and 4b.