The 1,4-cis-diethynylated a-d-mannopyranose analogue 11 has been prepared from 1,6 : 2,3-dianhydro-b-dallopyranose (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 4 C 1 and the other one a slightly distorted O S 2 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 4 C 1 conformation of the mannopyranosyl units (Fig. 2). The two butane fragments are characterised by a combination of gauche and antiperiplanar arrangements.Introduction. ± In the context of the synthesis of alkynylated saccharides, we have so far prepared up to hexadecameric cellulose analogues where the glycosidic O-atom is replaced by a butadiyne group, interrupting intramolecular, inter-residue H-bonds so as to evaluate their contribution to the supramolecular structure of cellulose (see [2] and earlier publications cited there). For this, we have synthesised glucopyranose derivatives possessing 1,4-trans-oriented ethynyl substituents [3] [4]. We have also synthesised the isomeric a-d-glucopyranose analogues, possessing 1,4-cis-oriented ethynyl substituents [5]. These have been incorporated in cyclotrimeric, cyclotetrameric, and cyclohexameric analogues of cyclodextrins [6]. Remarkably, oxidative oligomerisation of the dialkyne 1 has led in a single step to the C 1 -symmetric cyclotrimer 2 (Scheme 1), while the larger cyclooligomers were prepared by selective cross-coupling. We have also used 4-, or 1-monoethynylated glucopyranose derivatives to transform maltohexaose derivatives to maltooctaoses possessing terminal ethynyl groups, and further to cyclomaltooctaose analogues, in which a butadiyne-1,4-diyl group is replaced by one glycosidic O-atom [1].In the course of the synthesis of these acetyleno sugars, we have devised methods for the invertive [5] or retentive [3] alkynylating opening of 1,6-anhydro-b-dglucopyranoses, providing a rapid access to a-or b-d-glucopyranosyl-acetylenes. It was tempting to also prepare the analogous branched chain a-d-mannopyranosylacetylene and to examine its oxidative cyclooligomerisation. A few mannopyranosylacetylenes have been prepared [7 ± 10]. Reductive dehydroxylation of an ulose

F¸r Oskar Jeger mit herzlichen Gl¸ckw¸nschen zum 85. GeburtstagThe ethynylated gluco-azide 11 was prepared from the dianhydrogalactose 7 by ethynylation, transformation into the dianhydromannose 10, and opening of the oxirane ring by azide (Scheme 1). The retentive alkynylating ring opening of 11 and of the corresponding amine 12 failed. (2-Acetamidoglucopyranosyl)acetylenes were, therefore, prepared from the corresponding mannopyranosylacetylenes. Retentive alkynylating ring opening of the partially protected b-d-mannopyranose 15, possessing a C(3)ÀOH group, gave a 85 : 15 mixture of 16 and the (E)-enyne 17. The alkyne 16 was deprotected to the tetrol 18 that was selectively protected and transformed into the C(2)ÀO triflate 20. Treatment with NaN 3 in DMF afforded a 85 : 15 mixture of the b-dgluco configured azide 21 and the elimination product 22. Similarly, the a-d-mannopyranosylacetylene 23 was transformed into the azide 26. Retentive alkynylating ring opening of the ethynylated anhydromannose 28 gave the expected b-d-mannopyranosyl 1,4-dialkyne 29 as the main product besides the diol 28, the triol 31, and the (E)-enyne 30 (Scheme 2). This enyne was also obtained from 31 by a stereoselective carboalumination promoted by the cis (axial) HOÀC(2) group. Deprotection of the dialkynylated mannoside 31 led to 32, whereas selective silylation, triflation, and azidation gave a 3 : 7 mixture of the 1-ethynylglucal 35 and the b-d-gluco azide 36, which was transformed into the diethynylated b-d-GlcNAc analogue 38. Similarly, the diethynylated a-dmannopyranoside 39 was transformed into the disilylated a-d-GlcNAc analogue 41, and further into the diol 42 and the monosilyl ether 43 (Scheme 5). Eglinton coupling of 41 gave the symmetric buta-1,3-diyne 44, which did not undergo any further Eglinton coupling, even under forcing conditions. However, Eglinton coupling of the monosilyl ether 43 and subsequent desilylation gave the C 1 -symmetric cyclotrimer 45 in moderate yields.

Some new heterocyclic liquid-crystalline compounds incorporating a 1,3-disubstituted allene unit were synthesised. These axial-chiral compounds were investigated by polarisation microscopy and differential scanning calorimetry. One of them was also synthesised in enantiomerically enriched form by enantioselective synthesis. It was found that the latter product exhibits a ferroelectric switchable chiral smetic C phase with an unexpectedly large value of the spontaneous polarisation.Due to their special physical properties and the potential technical applications, chiral mesophases are a central topic in liquid crystal research [']. Especially materials that display the chiral smectic C phase are of particular interest because of their ferroelectric properties and their potential use for display device^ [^,^]. As is well-known, the ferroelectric properties of smectic liquic crystals are related to the chirality of the mesophase. Up to now most liquid crystals with chiral mesophases incorporate a centre of chirality. Only a few examples of mesogenic compounds that possess an axis or a plane of chirality have so far been reportedL4-']. In a project aimed at the synthesis of novel axial-chiral mesogenic compounds with ferroelectric properties, the first liquid crystalline allene derivatives, displaying chiral smectic C phases, were recently synthesised (e.g. compound l)[sl.1: cr 67 S ; 99 N' 100 BP 101 is In order to investigate the influence of changes in the substitution pattern of the allene moiety on the mesogenic behaviour and ferroelectric properties, we set out to synthesise a liquid-crystalline derivative of 2,3-undecadien-1-01 in which the methyl group of 1 is replaced by hydrogen. Our strategy was to prepare in a first step liquid-crystalline derivatives of readily available racemic 2,3-undecadien-l-o1. According to Scheme 1 the a-allenic alcohol ruc-6 was synthesised by starting from propargylic alcohol and was appended to several thiadiaz~le[~l and pyrimidine['0] phenol derivatives by the Mitsunobu etherificati~n['~.'~I to afford the mesogenic compounds rue-7a-d. In a second part the enantiomerically enriched allene derivative (R)-7a was prepared by a nine-step synthesis, starting from propargylic alcohol, in a total yield of 11% and with approximately 94Yn enantiomeric excess (Scheme 2). The propargylic alcohol ruc-3 was oxidised by the DessMartin peri~dinane ["-~~]. The resulting propargylic ketone 8 was treated with (R)-Alpine borane[201 to yield the optically active propargylic alcohol 3 in 95% ee after oxidation workup [2',2']. By comparison of the models for the diastereomeric transition states of the (R)-Alpine borane reduction of ketone 8, the absolute configuration R was assigned to the major enantiomer of propargylic alcohol 3L2l]. The compound (R)-3 was treated with methanesulfonyl chloride (MsCI). The resulting methanesulfonate (R)-9 was isolated and then treated with anhydrous hydrazine and subsequently with diethyl azodicarboxylate (DEAD) [24.25]. The a-allenic silyl ether 10 thus obtained wa...

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