Monoacylation diols

Mono cylDiols. Enzymatic synthesis of chiral monoacyl diols can be carried out either by direct enzymatic acylation of prochiral diols or by hydrolysis of chemically synthesized dicarboxylates. 

A number of examples of monoacylated diols produced by enzymatic hydrolysis of prochiral carboxylates are presented in Table 3. PLE-catalyzed conversions of acycHc diesters strongly depend on the stmcture of the substituent and are usually poor for alkyl derivatives. Lipases are much less sensitive to the stmcture of the side chain the yields and selectivity of the hydrolysis of both alkyl (26) and aryl (24) derivatives are similar. The enzyme selectivity depends not only on the stmcture of the alcohol, but also on the nature of the acyl moiety (48). 

An interest in ester migration in the monoacyl derivatives of the vicinal-diol grouping in ribofuranosides stemmed from a desire to establish the position of attachment of the aminoacyl group to the terminal adenosine residue of aminoacyl-(t-RNA),569-571 and also from the necessity of producing suitably protected intermediates for oligoribonucleotide syntheses. That a facile equilibrium can exist is shown by the fact that, on being kept, an ethanol solution of... 

Reginato, G. Ricci, A. Roelens, S. Scapecchi, S., Group 14 Organometallic Reagents.9. Organotin-Mediated Monoacylation of Diols with Reversed Chemoselectivity - a Conveiuent Synthetic Method. J. Org. Chem. 1990,55, 5132-5139. 

Rodens, S., Organotin-mediated monoacylation of diols with reversed chemoselectivity. Mechanism and selectivity. J. Org. Chem. 1996,61, 5257-5263. 

Monoacylation of achiral and meso diols has been a popular strategy for introducing asymmetry and, in addition to kinetic resolutions of secondary alcohols, a... 

The enantioselective enzyme (pig liver esterase)-catalyzed hydrolysis of a prostereogenic diester, such as dimethyl we.vo-4-oxocyclopentane-l,2-dicarboxylate, to give the chiral monoester 357,58 (for configurational assignment, see p441) or the enantioselective monoacylation of a prostereogenic diol. 

In contrast to the course of the Prevost Reaction, water appears to add readily as a nucleophile to the partially positive carbon atom of the intermediate. The cyclic orthoacetate is then cleaved to a monoacylated diol ... 

The monoacylation of symmetrical diols has been extensively investigated, and several useful methods have been developed. 1,2-Diols can be monoacylated readily, presumably because the product is acylated more slowly than the starting diol (Scheme 10.4). A variety of catalysts, for example lanthanide salts [10, 11], zeolites [12, 13], and tin derivatives [14, 15] have been used to further improve the selectivity of this reaction. Orthoesters have also been successfully used as acylating agents for the monoacylation of 1,2-diols [16],... 

Diols with more than two carbon atoms between the two hydroxyl groups may require more carefully controlled reaction conditions if a monoacylation is desired (Scheme 10.6). Suitable catalysts which promote the formation of monoacylated products include silica gel [21], zeolites [12], and tin(IV) derivatives [14, 22]. 

An alternative strategy for preparation of monoacylated 1,2- and 1,3-diols is oxidative deavage of cyclic acetals prepared from a diol and an aliphatic or aromatic aldehyde (Scheme 10.7). For this purpose the required acetal does not need to be isolated, but can be generated in situ [25]. Acetals prepared from strongly electrophilic aldehydes, for example nitrobenzaldehydes, will, however, usually be difficult to oxidize (and to hydrolyze). 

Scheme 10.7. Oxidative cleavage of acetals to yield monoacylated diols [26].

Diols can also be selectively monoacylated by treatment with an acylating agent of low reactivity (vinyl, 2,2,2-trifluoroethyl, phenyl, or ethyl esters) in the presence of catalytic amounts of an esterase (Scheme 10.8) [27]. Surprisingly, these enzymatic... 

Clarke, P. A. Selective monoacylation of meso-and C2-symmetric 1,3- and 1,4-diols. Tetrahedron Lett. 2002, 43, 4761 1763. 

Ogawa, H. Amano, M. Chihara, T. Facile and highly selective monoacylation of symmetric diols adsorbed on silica gel with MeCOCl. Chem. Commun. 1998, 495—496. 

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... 

Conversion ofpropargyl esters to dihydrofurans1 (11,469-470). The reaction can be used for an enantioselective synthesis of dihydrofurans. Thus reduction of 3-hydroxy-l-alkynyl ketones (2) with Midland s reagent, (+)-l, provides (4S)-2-bu-tyne-l,4-diols (3) in 84-91% ee. Monoacylation (4) followed by treatment with... 

An alternative method was offered by Woodward who was able to perform the monoacylation of the diol and consequently performed the rearrangement to 0,S binaphthol (Scheme 30) [79]. 

A total synthesis of 1,3-dideoxynojirimycin starting from cyclopentadiene was proposed by Johnson et al. [206]. Photooxidation of cyclopentadiene and reductive workup with thiourea generates c/ -cyclopent-2-ene-l,4-diol, which is monoacylated with high enantioselectivity (>99% ee) with isoprenyl acetate and Candida antarctica lipase B (Novo Nordisk SP 435) to give 461. After silylation of 461 and subsequent treatment with KOH and oxidation, enantiomerically pure enone 462 is obtained [207]. 

The reaction can also be run using catalytic amounts of a tin reagent which results in acylation of the least hindered alcohol or monoacylation of symmetrical diols is also possible. The use of a chiral tin reagent gives modest levels of kinetic resolution of racemic diols. ... 

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