Abstract
The 1,4-cis-diethynylated α-D-mannopyranose analogue 11 has been prepared from 1,6 : 2,3-dianhydro-β-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(methanesulfonate) 19 revealed substantially bent butadiyne moieties; one mannopyranosyl ring adopts the 4C1 and the other one a slightly distorted OS2 conformation (Fig. 1). Hydrogenation of 18, followed by deprotection, gave the stable butane-1,4-diyl-bridged cyclodimer 21 (Scheme 3). Crystal-structure analysis shows the 4C1 conformation of the mannopyranosyl units (Fig. 2). The two butane fragments are characterised by a combination of gauche and antiperiplanar arrangements.
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