Diastereoselective Functionalization of a Spherand‐Type Calixarene

Abstract

AbstractCondensation of 5,5′‐di‐tert‐butyl‐2,2′‐dihydroxybiphenyl (1) with formaldehyde yields a cyclic trimer 2 (and tetramer 3) having three (four) methylene groups less than a calix[6]‐arene (calix[8]arene). Alkylation of the (flexible) trimer with ethyl bromoacetate gives exclusively the stereoisomer 4 with C2 symmetry, while the isomer with D3 symmetry is not observed. Two isomers 6a and 6b (C2 and C1 symmetry) are obtained by treatment with tert‐butyl bromoacetate which both are converted by transesterification with methanol into the same hexamethyl ester 5 having C2 symmetry. These results are rationalized by restricted rotation around ArAr bonds for larger O‐alkyl groups also around ArCH2Ar bonds. The structure of the hexaethyl ester 4 is also confirmed by single crystal X‐ray analysis.