Diastereoselective Lower Rim (1S)-Camphorsulfonylation as the Shortest Way to the Inherently Chiral Calix[4]arene

Abstract

[structure: see text]. A diastereomeric mixture of chiral 25-(1S)-camphorsulfonyloxy-26-isopropoxycalix[4]arene 2a (de 15%) and 25-isopropoxy-26-((1S)-10-camphorsulfonyl)calix[4]arene 2b has been obtained by asymmetrical lower rim (1S)-camphorsulfonylation of the monoisopropoxycalix[4]arene. Pure diastereomer 2a has been obtained by simple crystallization, and its absolute configuration has been determinated by X-ray analysis. Enantiomerically pure inherently chiral 5,11-dibromo-26-isopropoxycalix[4]arene 4 has been synthesized by the upper rim dibromination of the diastereomer 2a followed by hydrolytical removal of the auxiliary camphorsulfonyl group.

Synthesis and conformational studies of calixarene analogue chiral [3.3.1]metacyclophanes

“…Inherently chiral calixarenes are unusual types of chiral calixarenes which are not based on a chiral subunit but are due to the absence of a plane of symmetry or an inversion center in the molecule [22e25]. Inherently chiral calixarenes are considered as promising host molecules for molecular recognition [26,27] and as asymmetric catalysts [17]. A large number of racemic, inherently chiral calixarenes have been reported and some of them have been resolved into the enantiomerically pure form [22e25].…”

Upper-rim calixarene phosphines consisting of multiple lower-rim OH functional groups: synthesis and characterisation

“…This diastereotopic splitting is due to the preserved inherent chirality present in 4. The chemical shift of the hydroxyl proton at 8.77 ppm suggests its participation in an intramolecular hydrogen bond (17) with neighbouring oxygen atoms on the lower rim. The 31 P NMR spectrum of 4 consists of three closely spaced multiplets at 27.47, 28.30 and 28.86 ppm in a ratio of 1:1:1, and these resonances correspond to distinct phosphine oxide groups.…”

Enantiopure inherently chiral calix[4]arene derivatives containing quinolin-2-yl-methanol moiety: Synthesis and application in the catalytic asymmetric addition of diethylzinc to benzaldehyde

“…Although considerable efforts were made to synthesize inherently chiral calixarenes during the past two decades, their optical resolutions were usually realized by HPLC method [1,2] , which is inappropriate for scale-up， thus impeding their practical applications. As a result, few reports on the applications of inherently chiral calixarenes in chiral molecular recognition [4,5] and asymmetric catalysis [5,6] have been hitherto reported. We [7][8][9][10][11] have recently reported an efficient approach to the synthesis of enantiopure inherently chiral calix [4] crowns by introduction of a chiral auxiliary and then separation of subsequent diastereomers via preparative TLC or even column chromatography on silica gel, and further found [10] that a tetra-O-alkylated inherently chiral fluorescent calix [4]crown-6 in the partial cone conformation could show considerable enantioselective recognition capability towards chiral leucinol.…”