Diols by acylation

In an early example of the desymmetrization of meso-diols by acylation Duhamel... 

Catalytic asymmetric sulfonylation, which is clearly more directly comparable with the above-described work involving KR and ASD of racemic secondary alcohols and 1,2-diols by acylation and phosphorylation, has received attention only very recently. Some work has been carried out by Onomura et al. into catalytic ASD of meso-1,2-diols by monosulfonylation [97] and the sulfonylative KR of racemic 2-hydroxyalkanamides [98, 99] catalyzed by chiral copper-BOX type Lewis acids, but only one report by the Miller group addresses nucleophile-catalyzed asymmetric sulfonylation. 

Analogously, the 2R-isomer yield 85%, and diastereomeric mixture yield 82%, were obtained by acylation of the corresponding diols. 

Preparation of polycyclic ortho esters and hydrogen ortho esters by acylation of diols and triols [164-170]. 

Desymmetrization of some phosphorus derivatives has been achieved (Scheme 4.15). Thus, the monoacetate 21 can be obtained from the corresponding diol by PFL-catalyzed acylation with vinyl acetate in chloroform [60]. The monoacetate 22 can be obtained from the corresponding bis(hydroxymethyl)phenylphosphine borane by acylation of the latter in vinyl acetate mediated by CALB [61]. 

Hydrolase-catalyzed desymmetrizations of meso-diols have also been exploited (Scheme 4.16). Thus, the monoacetate 23 is produced in excellent yield and by acylation with vinyl acetate of the corresponding meso-diol catalyzed by CRL in hexane [62]. In a similar way the monoacetate 24 is produced from the meso-tetrol by acylation in vinyl acetate catalyzed by PPL [63]. The meso-piperidine derivative... 

Kinetic resolution of racemic alcohols by acylation Few steps from chiral diols... 

Monoacylation of diols.1 Monoacylation of unsymmetrical 1,2-, 1,3-, and 1,4-diols can be effected by acylation of the dibutylstannylene derivatives, followed by quenching with oxalic acid or ClSi(CH3)2C6H5. This process effects monoacylation of the more-substituted hydroxyl group, even a tertiary one. This method also is... 

Rings containing unsaturation may be synthesized from fragments in higher oxidation states. l,3-Dioxolan-2-ylium cations are obtained directly from tertiary 1,2-diols and acyl cations in excellent yields (80ZOR183). The reaction, shown in equation (37), is limited to tertiary alcohols since steric hinderance prevents nucleophilic ring opening by the counterion. Another synthesis of limited scope is the addition of monothiobenzils to diaryl-diazomethanes (equation 38). The reaction also works for the dicarbonyl derivatives. 

Reaction of this fucose derivative with the glucosyl donor 54 (oe 3 2 1) in the presence of catalytic amounts of BF3 Et20 cleanly provided the desired p-configurated disaccharide 55. Deprotection followed by acylation of the resulting diol 55a with 6-heptenoic acid in the presence of DCC and DMAP... 

Selective alkylation and acylation of a vic-diol. Selective acylation or alkylation of cyclohexanoid, axial-equatorial oic-diols is possible by way of the dibutyl-itannylene derivative, obtained by reaction with bis(tri-n-butyltin) oxide. A typical reaction is formulated for a myo-inositol derivative in equation (1). The method... 

Asymmetric Acylation of me o-Diols. Both cyclic and acyclic me o-1,2-diols are desymmetrized by acylation in the presence of a stoichiometric amount of this ligand with modest-to-excellent enantioselectivity (eq 4). In a special case, cis-5,5-dimethyl-2-cyclopentene-l,4-dior was monobenzoylated in the presence of a catalytic amount of this ligand in good yield and with perfect enantioselection (87%, >99.5% ee). 

Bridged or reinforced azamacrocycles, which have pairs of nitrogen atoms of an aza-macrocycle linked, usually by an a,cu-alkandiyl bridge, 154 are prepared by reaction of a cyclic amine with a bifunctional nucleophile, such as an a,cu-dibromoalkane or an a,cu-ditosyl-alkane-diol. Bis(acyl esters), amides, and halides react with amines to form bicyclic amides which can be reduced to the bicyclic amines.155 The bridge can have internal functions, such as C=C or o-C6H4 (or include hetero atoms, thus forming clathrochelates).156... 

Mixed primary secondary diols are very often separated into their enantiomers in a sequential two-step acylation wherein the first step - acylation of the primary hydroxyl group - shows high regio- but very poor enantioselectivity. The useful enantiomer-differentiating step is realized in the second step by acylation of the already monoacylated diol (31—36, 46, 72,107—110,120, 125). On the other hand, as expected, mixed primary tertiary diols are not acylated at the tertiary hydroxyl group (47, 48, 51-54, 56-62,106). 

An Italian group [51,52] showed that an alternative method, the Sharpless enantioselective dihydroxylation [53], was an efficient procedure for the preparation of AB block (J )-10. Thus enone 37, obtained by acylation (Acf l-AlCb) of dihydronaphthalene 36 [54], on treatment with the enriched (1% K2OSO4 2H2O) AD-mix-a [55] gave diol 38 in 71% yield and 98% ee (Scheme 7). Reaction of 38 with trimethylorthoacetate and subsequent treatment of the intermediate cyclic orthoester with trimethylsilyl chloride afforded chloroacetate 39. Reduction of 39 with tributyltin hydride, followed by hydrolysis, furnished enantiopure (R)-IO in 52% overall yield (from 37). 

A Wittig reaction of the ylide 294 with the aldehyde 289 formed the backbone 295, which was then treated with trifluoroacetic acid to remove the acetonide, followed by acylation of the diol with the (-)-TCA segment 296 (248). Hydrogenatirai of the alkene and hydrogenolysis of all benzyl protecting groups with H2 (1 atm) and Pearlman s catalyst afforded fumonisin B2 (250) (Scheme 5.6). 

Scheme 22.7 Remote desymmetrisation of a a-symmetric diol 32 by acylation with Miller s peptide-based iV-methylimidazole catalyst 33.

Insoluble polymers containing pendant trityl chloride groups have been used to block one of the primary hydroxy-groups of symmetrical aa>-dioIs and simple polyhydroxy-compounds. Acetylation or benzoylation followed by acid cleavage from the polymer yielded monoesterified products from the diols, although acyl migration occurred on similar treatment of some polyhydroxy-compounds. 

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