Cyclohexanoid

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... 

Reaction of the D-galacto homologue of 80 with l-acetoxypyridin-2(l//)-thione under the influence of light resulted in cyclohexanoids 96. ... 

The formation of the cyclohexanoid ring from an acyclic precursor requires a syn- or Z-conformation either in the ground state or in the activated complex. On a basis of this argument, formerly it was thought that NPP, the Z-isomer of GPP, was the most likely precursor of cyclic monoterpenes. However, it is now known that GPP is the preferred precursor. Recent studies with cell-free systems indicate that GPP can be converted into cyclic products without detectable conversion into any other acyclic intermediates (Croteau, 1984, 1987 Johnson and Croteau, 1987). 

The cyclohexanoid category of monoterpenes contains the greatest number of individual compounds and forms the primary focus of the present re-... 

Representative diterpene structures are shown in Fig. 18. Diterpenes can be classified on a biogenetic basis (Ruzicka et al., 1953 McCrindle and Overton, 1965 Hanson, 1972a). There are a few open-chain diterpenes. Phy-tol, in an ester linkage, is found as a side chain on the chlorophyll molecule. Most diterpenes are cyclic compounds. A few diterpenes are formed by cy-clizations analogous to those involved in the synthesis of cyclohexanoid monoterpenes. The result is a macrocyclic structure such as that of cem-... 

Aliphatic or cyclohexanoid monoterpenes originate from geranyl pyrophosphate (D 6) and/or neryl pyrophosphate probably formed by different prenyltrans-ferases. Of significance are the following types of reactions ... 

Acyclic monoterpenes, e.g., myrcene, and cyclohexanoid congeners, e.g., limonene, a- and P-pinenes, camphene... 

Several of these products [189-191] have been prepared and used for the total synthesis of natural products [185-187]. The formation of by-products was observed quite often during these reductions. This might be due to the slow rates of the reaction. Hence, the addition of activators has been suggested [191]. These "activators" (most often a,p-imsaturated alcohols, ketones, or nitriles) seem to act as suicide substrates for several oxidoreductases [192, 193], whereas, for the reduction of cyclopentanoid 1,3-diketones, stereoselectivity was high, and most often [194] low selectivity was observed for cyclohexanoid 1,3-diketones [184, 194-197]. 

Babler, J. H., and M. J. Coghlan Facile method for bishomologation of ketones to a,P-unsaturated aldehydes. Application to synthesis of cyclohexanoid components of the boll wevil sex pheromone. Synth. Commun. 6,469—474 (1976). 

The reduction of cyclic 2,2-disubstituted 1,3-diketones 136 (Fig. 38) can be regarded as an example of an enzyme-catalyzed distinction of a substrate containing two trigonal carbonyl centers with stereotopic faces and one prochiral tetrahedral carbon center where monoreduction generates two chiral centers. All of the products 137 and 138 were obtained with high e.e. [173-185]. Cyclohexanoid 1,3-diketones have been reduced with low dia-stereoselectivity as compared to the cyclopentanoid series [173,184,186-196]. Dimeriza tion under participation of acetaldehyde produced by fermenting yeast has occasionally... 

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