Cyclohexane derivatives dithiane derivative

For the 1,4-dithiane skeleton, two S-alkyl-l,4-dithianium salts 72 and 73 were studied by variable temperature NMR spectroscopy in the solid state (13C CP-MAS) (99JMS93) line shape variations were attributed to the conformational motion of the six-membered ring (cf. Scheme 26). Also, the vibrational frequencies of the 1,4-dithiane derivative were analysed in detail it was corroborated that the molecule exists in the C2h configuration similar to the chair form of cyclohexane (99SA(A)121). 

Carbon-13 shift values of parent heterocycloalkanes [408] collected in Table 4.61 are essentally determined by the heteroatom electronegativity, in analogy to the behavior of open-chain ethers, acetals, thioethers, thioacetals, secondary and tertiary amines. Similarly to cyclopropanes, three-membered heterocycloalkanes (oxirane, thiirane, and azirane derivatives) display outstandingly small carbon-13 shift values due to their particular bonding state. Empirical increment systems based on eq. (4.1) permit shift predictions of alkyl- and phenyl-substituted oxiranes [409] and of methyl-substituted tetrahydropyrans, tetrahydrothiapyrans, piperidines, 1,3-dithianes, and 1,3-oxathianes [408], respectively. Methyl increments of these heterocycloalkanes are closely related to those derived for cyclohexane (Table 4.7) due to common structural features of six-membered rings. 

The preparation of the bisthioketal of cyclohexane-1,3-dione (25) illustrates the use of 2-lithio-1,3-dithiane for synthesis of cyclic diketones. The lithio derivative (2) is transformed as above into the bisdithiane (24), which is then heated successively with n-butyllithium, l-iodo-3-chloropropane, and finally /i-butyllithium.8... 

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