Acylation polyol

Complexes of 3-acetyl-2-oxazolone (20) and organozirconium compounds have been found to acylate polyols with excellent... 

Miller also explored the ASD of glycerol derivatives through an enantioselective acylation process which relies on the use of a pentapeptide-catalyst which incorporates an A-terminal nucleophilic 3-(l-imidazolyl)-(5)-alanine residue [171], Most recently, Miller has probed in detail the role of dihedral angle restriction within a peptide-based catalyst for ferf-alcohol KR [172], site selective acylation of erythromycin A [173], and site selective catalysis of phenyl thionoformate transfer in polyols to allow regioselective Barton-McCombie deoxygenation [174],... 

Natural polyols have been used as substrates for the so-called combinatorial biocatalysis , a proposed approach to drug discovery [33]. For instance, complementary enzymatic regioselectivity was applied to produce a combinatorial library of 167 distinct selectively acylated derivatives of the flavonoid bergenin (11) on a robotic workstation [34]. Another lead compound, the antitumoral paclitaxel (12, a molecule with very low water solubility) has been similarly derivatized, initially exploiting the selectivity of the protease thermolysin for its side-chain C-2 OH. 

By acetolysis of a- or /3-methylene acetals of polyols with trifluoroacetic anhydride-carboxylic acid mixtures, derivatives may be prepared71 that are O-acylated at the primary hydroxyl group, and that have free hydroxyl groups at certain secondary positions. 

Liming successfully attached a concave arrangement of pyridine units to Fre-chet-type dendrimers in homogeneous phase. A remarkable selectivity was thus achieved in base-catalysed addition of ketenes to alcohols and polyols (e.g. monosaccharides). The functionalised dendrimer catalysts exhibit a greater molar mass than conventional non-dendritic catalysts, thus permitting subsequent recycling of the catalyst by nanofiltration. These dendrimers are thus suitable as reagents for selective acylation of polyols [4]. 

Alkyl nitrates (V), particularly polyol nitrates (V) such as nitrocellulose and nitroglycerine Alkyl and acyl nitrites (III)... 

In general reaction of an alcohol with the appropriate anhydride or acid chloride in pyridine at 0-20 JC is sufficient. In the case of tertiary alcohols, acylation is very slow in which case a catalytic amount of 4-dimethylaminopyridine (DMAP) can be added to speed up the reaction by a factor of 10,000. Reaction of polyols with acyl chlorides (1.2 equiv) in the presence of hindered bases (2.0equiv) such as 2,4,6-collidine, diisopropylethylamine or 1,2,2,6,6-penta-methylpiperidine in dichloromethane at -78 °C leads to selective acylation of a primary alcohol. Primary alcohols can also be acylated selectively with isopro-penyl acetate or acetic anhydride in the presence of a catalytic amount of 1,3-dichlorotetrabutyldistannoxane 325.1 [Scheme 4.325].602 The catalyst 325.1 is available commercially or can be easily prepared by simply mixing dibutyltin oxide and dibutyldichlorostannane. No aqueous workup is necessary since the catalyst can be removed by simple chromatography. 

Amino-polyols, such as 1-aminodeoxy-D-sorbitol or D-(-l-)-glucosamine, as well as adenine, underwent selenenylation-acylation at the amino groups by dichloride 102 and thus their 2-benzisoselenazol-3(2//)-onyl derivatives 108 and 109 were obtained <2003SC1301> (Scheme 40). The organoselenium-modified /3-CDs 110 and 111 were synthesized in a similar way <2002HCA9>. 

Selective activation of hydroxyl groups by the stannylation procedure is an established practice to efficiently manipulate diols and polyols [53, 54]. Among the various reagents and methods, activation through dialkylstannylene acetals is noteworthy. This two-step protection method involves the conversion of dihydroxy substrates into cyclic dialkyl dioxastan-nanes which, in turn, are treated with suitable nucleophiles, to regioselectively afford the corresponding mono alkyl, silyl or acyl derivatives under neutral conditions. 

The 1,3-polyol system is prevalent in a variety of marine natural products. This interesting arrangement of hydroxyl groups can be assembled using aldehydes 574, 575, and 1,3-dithiane as an acyl anion equivalent (Scheme 83) [138]. 

Herradon also described the acylation of polyols [41] and amino alcohols (Scheme 5.6) [42] catalyzed by dibutyltin oxide. The chemoselectivity of the reaction depends on the power applied during irradiation. 

U. Liining, W. Hacker, Concave reagents, 31 a Merrifield bonnd concave Pyridine for the selective acylation of polyols, J. Prakt. Chem., 1999, 341, 662—667. 

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