Syntheses of inherently chiral monosulfinyltrithiacalix[4]arenes by the oxidation of one of the bridging sulfurs of a tetrathiacalix[4]arene fixed in the 1,3-alternate conformation

A new synthetic strategy for the construction of an inherently chiral, sulfur-bridged calix[4]arene molecular framework was presented by oxidation of one of the four epithio bonds of a tetrathiacalix[4]arene derivative of 1,3-alternate conformation: Tetra(carboxymethyl) ether of p-tert-butyltetrathiacalix[4]arene of 1,3-alternate conformation (7) was converted to the tetra(l-menthoxycarbonylmethyl) ether (8). Oxidation of the tetra l-menthyl ester 8 by treatment with NaBO₃ (1.1 molar equiv.) afforded a pair of diastereomers of the monosulfinyl derivatives (9) in 58% yield, which were readily separable by silica-gel column chromatography. Removal of the l-menthyl moieties followed by methyl esterification gave enantiomerically pure samples of inherently chiral (-)- and (+)-monosulfmyltrithiacalix[4]arene derivatives ((-)-10 and (+)-10) in 62 and 56% yield, respectively.