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 calix4]arene molecular framework was presented by oxidation of one of the four epithio bonds of a tetrathiacalix4]arene derivative of 1,3-alternate conformation: Tetra(carboxymethyl) ether of p-tert-butyltetrathiacalix4]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 (+)-monosulfinyltrithiacalix4]arene derivatives ((-) -10 and (+) -10 ) in 62 and 56% yield, respectively.