Oligosaccharide analogues of polysaccharides Part 23 synthesis of a dimeric acetyleno cyclodextrin from a mannopyranose-derived dialkyne

The 1,4-cis-diethynylated alpha -D-mannopyranose analogue 11 has been prepa red from 1,6:2,3-dianhydro-beta -D-allopyranose (6) by alkynylating epoxide and acetal opening (Scheme 2). Eglinton coupling of 11 gave the cyclodimer 18 (Scheme 3). Crystal-structure analysis of the corresponding bis(methane sulfonate) 19 revealed substantially bent butadiyne moieties; one mannopyra nosyl ring adopts the C-4(1) and the other one a slightly distorted S-O(2) conformation (Fig. 1). Hydrogenation of 18, followed by deprotection, gave the stable butane-1,4-diyl-bridged cyclodimer 21 (Scheme 3). Crystal-struct ure analysis shows the C-4(1) conformation of the mannopyranosyl units (Fig . 2). The two butane fragments are characterised by a combination of gauche and antiperiplanar arrangements.