Monobenzoylated diol

Significantly improved results were obtained in 2003 by employing the phosphi-nite derivative 22 of cinchonine as a catalyst, which can be obtained as a mixture with the undesired corresponding phosphinate from the reaction of cinchonine (1) and chlorodiphenylphosphane [30a]. The desymmetrization reaction of a range of 1,2-meso-diols with benzoyl chloride in the presence of 30 mol% of the phosphinite 22 as a mixture containing about 15% phosphinate afforded the corresponding monobenzoylated diol in excellent yields and ee values (up to 94% ee) (Scheme 11.15). It was postulated by the authors that the reaction is initiated by the activation of the... 

The enantioselective acylation proceeded with 34% yield of the monobenzoylated diol in 74% ee. The diastereomeric cinchonine phosphinite 85b gave nearly quantitative yield and 82% ee. Further studies with other me50-l,2-diols proceeded also in... 

Iwasaki, F. Maki, T. Onomura, O. Naka-shima, W. Matsumura, Y. Chemo- and stereoselective monobenzoylation of 1,2-diols catalyzed by organotin compounds. J. Org. Chem. 2000, 65, 996-1002. 

The 1,1-binaphthyl ring system is a key component of a number of chiral ligands that have been used as catalysts for asymmetric synthesis <1992S503>. Chemo- and stereoselective (. )-stannepin-catalyzed monobenzoylation of terminal 1,2-diols 312 afforded ( -enantiomer-enriched 2-benzoylated diols 313 in moderate selectivity. Only a trace of 1-benzoylated diols 314 was observed (Equation 55). Thus, the method was successfully applied to kinetic resolution of racemic 1-phenyl-1,2-ethanol using a chiral organotin catalyst <2000JOC996>. 

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). 

The catalytic efficiency of the diamines, 24 and 25, derived from the truncated cinchona alkaloids, quincorine and quincoridine, respectively, for the desymmetrization of meso- 1,4-diols was also investigated by Kiindig and coworkers [31a, b[. Both pseudoenantiomers 24 and 25 efficiently catalyzed the desymmetrization of the meso-complex 26 with benzoyl chloride, giving the enantiopure monobenzoylated Cr (CO)3 complexes, 27 and ent-27, respectively, with up to 99% ee (Scheme 11.17). This process will provide easy access to new planar chiral complexes. 

The use of chiral amines will selectively monobenzoylate a diol and simultaneously generate a chiral product with reasonable ee s. ... 

Monobenzoylation. 1,2-Diols form monobenzoates on reaction with BzCl and MejSnCE. 

In contrast, bromine could be introduced selectively in unprotected 1,5-an-hydroalditols by way of acyloxonium ions. The prerequisite for the formation of such ions was the presence of a 1,2-cA-diol motif. This concept had previously been shown by B. T. Golding and coworkers through treatment of cis and tram-1,2-dihydroxycyclohexanes with hydrogen bromide in acetic acid. The cis-, 2-diol gave the trans bromo acetate, whereas no bromine was introduced into the trans-, 2-diol under similar reaction conditions only acetylation occurred. Pedersen showed furthermore that monobenzoylated cis- and trans-, 2-di-hydroxycyclohexanes gave analogous results. 

Maki T, Iwasaki F, Matsumura Y (1998) A new convenient method for selective monobenzoylation of diols. Tetrahedron Lett 39 5601... 

Acylations Carbon-coated magnetic Co-nanoparticles tagged with azabis (oxazoline)-Cu(II) complexes were utilized in a Cu(I)-catalyzed azide/alkyne cycloaddition (CuAAC), and the efficacy of the resulting nanomagnetic catalyst was tested in the kinetic resolution (KR) of racemic l,2-diphenylethane-l,2-diol via asymmetric monobenzoylation under batch conditions and in a continuous flow-type reactor [39]. 

In 2008, Kiindig et al. [74] developed a low molecular weight quincorine-derived chiral catalyst for the asymmetric monobenzoylation of cyclic and acyclic meso 1,2-diols, affording ees ranging from 34% to 97% (Scheme 41.26). The rationale behind the design of their catalyst relied on the use of two tertiary amine moieties, one of which would function as an acyl activator while the... 

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