Cyclohexane compounds with different substituents

An interesting photochemical formation of different 1,4-dihydro-1,3,5-triazines (168-171) was demonstrated by Kobayashi et al.261 who irradiated substituted 1,3,5-triazines (167) of low aromaticity in pentane or cyclohexane, utilizing compounds with two different fluoroalkyl groups on the triazine ring. Two or three distinct products were isolated, the ratio of these dihydro compounds depending on the nature of both substituents and the solvent (which also serves as a reagent) [Eq. (82)].267... 

Aromatic compounds can be transformed into substituted cyclohexanes by catalytic hydrogenation. The nature of the substituents on the aromatic ring plays an important role, especially in regard to the ease of ring hydrogenation. The effect of die substituents is not the same for all catalytic systems. Thus, the following orders of reactivity are observed with the different catalysts1" 4 ... 

The A value, the free-energy difference between the two chair conformations with axial and equatorial alkyl groups, is widely used as a measure of steric size . For all alkyl groups there is less than 7% of the axial conformation present at ambient temperature and direct quantitative observation of the equilibrium is not possible. Historically, indirect examination of conformational equilibria in disubstituted cyclohexanes has been used to predict equilibria in monoalkyl compounds (assuming additivity of substituent effects), and reviews of early work in this field and of the pitfalls encountered have been given... 

Recognition of the vinyl acetal character of hex-5-enopyranosides and of the convertibility of such compounds by reductive rearrangement to carbocyclic products by treatment with triisobutylaluminium led to the modified route to cyclohexanes from 6-deoxyhex-5-enoside derivatives illustrated in Scheme 9 [43]. In this way compound 43 is converted in 79% yield to the deoxyino-sitol 44, there being two important differences relative to the mercury(II)-pro-moted ring closure the anomeric centre substituent is retained, and specific reduction is effected at the carbonyl centre. From the )0-anomer of compound... 

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