The glucose‐, mannose‐, and galactose‐derived spirocyclic cyclopropylammonium chlorides 1a–1d, 2a–2d and 3a–3d were prepared as potential glycosidase inhibitors. Cyclopropanation of the diazirine 5 with ethyl acrylate led in 71% yield to a 4 : 5 : 1 : 20 mixture of the ethyl cyclopropanecarboxylates 7a–7d, while the Cu‐catalysed cycloaddition of ethyl diazoacetate to the exo‐glycal 6 afforded 7a–7d (6 : 2 : 5 : 3) in 93–98% yield (Scheme 1). Saponification, Curtius degradation, and subsequent addition of BnOH or t‐BuOH led in 60–80% overall yield to the Z‐ or Boc‐carbamates 11a–11d and 12a–12d, respectively. Hydrogenolysis of 11a–11d afforded 1a–1d, while 12a–12d was debenzylated to 13a–13d prior to acidic cleavage of the N‐Boc group. The manno‐ and galacto‐isomers 2a–2d and 3a–3d, respectively, were similarly obtained in comparable yields (Schemes 2 and 4). Also prepared were the differentially protected manno‐configured esters 24a–24d; they are intermediates for the synthesis of analogous N‐acetylglucosamine‐derived cyclopropanes (Scheme 3). The cyclopropylammonium chlorides 1a–1d, 2a–2d and 3a–3d are very weak inhibitors of several glycosidases (Tables 1 and 2). Traces of Pd compounds, however, generated upon catalytic debenzylation, proved to be strong inhibitors. PdCl$\rm{_{4}^{2-}}$ is, indeed, a reversible, micromolar inhibitor for the β‐glucosidases from C. saccharolyticum and sweet almonds (non‐competitive), the β‐galactosidases from bovine liver and from E. coli (both non‐competitive), the α‐galactosidase from Aspergillus niger (competitive), and an irreversible inhibitor of the α‐glucosidase from yeast and the α‐galactosidase from coffee beans. The cyclopropylamines derived from 1a–1d or 3a–3d significantly enhance the inhibition of the β‐glucosidase from C. saccharolyticum by PdCl$\rm{_{4}^{2-}}$, lowering the Ki value from 40 μM (PdCl$\rm{_{4}^{2-}}$) to 0.5 μM for a 1 : 1 mixture of PdCl$\rm{_{4}^{2-}}$ and 1d. A similar effect is shown by cyclopropylamine, but not by several other amines.

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The crystal structure of 1,5-anhydro-2,3,4,6-tetra-O-benzyl-1-hydrazi-d-glucitol (2) is reported and compared with the structures of other diaziridines. It is the first crystal structure of an N,N-unsubstituted diaziridine, noncoordinated at the N-atom, and the first crystal structure of a C-alkoxy-diaziridine. Although there is considerable shortening of the C(5)OÀC(1) bond, there is no asymmetry in the C(1)ÀN bond length, the C(5)O, C(1), C(2) plane bisecting the NÀN bond. The C(1)ÀN bonds appear to be slightly shorter and the NÀN bond longer than the average for diaziridines, although the structural data for diaziridines do not lend themselves to unequivocal interpretation.

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The title compounds, (-)-2 and (+)-2, representing potentially valuable building blocks for chemical synthesis, have each been prepared from cyclopentanone in eight steps. The pivotal one involves a resolution, through the quinine-or quinidine-promoted methanolysis of the cyclic anhydride (±)-10, leading to chromatographically separable pairs of enantiomerically pure forms of regio-isomeric methyl half-esters. Figure 1: The enzymatically-derived cis-1,2-dihydrocatechol 1 and the targeted analogues (-)-2 and (+)-2 RESULTS AND DISCUSSION The Synthesis of Compound (±)-2The synthetic sequence leading to the key bromocyclopentadiene required for accessing the initial target compound (±)-2 started (Scheme 1) with the conversion of cyclopentanone (3) into the corresponding dimethyl ketal 4 5 (62%) that was itself subjected to bromination and so forming the previously reported tribromide (±)-5 6 (58%) together with small amounts of the chromatographically separable cis-and trans-2,5-dibromo-1,1-dimethoxycyclopentanes.Scheme 1: Synthesis of the cyclopentadiene 6 and its participation in a Diels-Alder dimerization reaction.The structure of compound (±)-5 was confirmed by single-crystal X-ray crystallography (see Experimental Section and Supporting Information -SI -for details). After extensive experimentation it was determined that the best means for effecting the two-fold dehydrobromination of tribromide (±)-5 involved its exposure to potassium tert-butoxide in THF at 0 °C for 0.25 h. By such means, and after extractive work-up, a ca. 0.025 M solution of diene 6 6,7 (>80%) in hexane was obtained. On standing this rather reactive material was converted, via a Diels-Alder dimerization, into compound (±)-7 (variable yields) that hydrolyzed on standing togive enone (±)-8 8 (69% from 6). The structures of both compounds (±)-7 and (±)-8 were also confirmed by single-crystal X-ray analysis (see Experimental Section and SI for details).Despite its propensity to dimerize, diene 6 could be engaged in a Diels-Alder reaction, at 23 °C, with maleic anhydride (9) (Scheme 2) and so affording the expected adduct (±)-10 in 74% yield and the structure of which was also confirmed by single-crystal X-ray analysis. Hydrolysis of the ketal residue associated with the last compound was best accomplished using aluminium trichloride in dichloromethane and after extractive work-up the anticipated ketone (±)-11 was obtained in 68% yield and as a crystalline solid so the structure was again confirmed by singlecrystal X-ray analysis. On heating in refluxing o-xylene compound (±)-11 engaged in chelotropic extrusion of carbon monoxide 9 and thereby forming the anticipated diene (±)-12 (78%) that could be purified by kugelrohr distillation although on prolonged exposure to high temperatures it underwent Diels-Alder dimerization to give compound (±)-13 in varying yields.Scheme 2: Elaboration of cyclopentadiene 6 to the cyclic anhydride (±)-12Various efforts were made to adapt the chemistry outlined in Scheme 2 to the preparation of the diester (±)-2. The...