Underwood, Joseph Mark (1989) New methods in ring synthesis. University of Southampton, Doctoral Thesis.
Abstract
The synthesis and cyclisation of 3-methyl-4-methylene-3-(3-diazo-3-methoxycarbonyl-2-oxopropyl)-1-cyclohexanone,1-ethylene acetal is described in chapter one. A carbene insertion reaction was successful giving the tricycle 8,8-ethylenedioxy-3-methoxycarbonyl-6-methyl-4-oxotricyclo[4.4.0.01,3] decane, an intermediate in a projected synthesis of the quassinoid klaineanone. A comprehensive review of the methods for the construction of spiroacetals and fused cyclic ethers (relating to the 1,5-dioxadecalin type of structural unit) is presented in chapter two. In chapter three, the chemistry of allenyl sulphoxides is developed into a new synthesis of spiroacetals. The intramolecular base catalysed cyclisation of 4-methyl-6-phenylsulphinyl-4,5-hexadien-1-ol gave the dihydropyran 5-methyl-6-(phenylsulphinylmethyl)-3,4-dihydro-2H-pyran which is also an allylic sulphoxide. Alkylation of this compound with 3-iodopropoxy(tert-butyldimethyl)silane followed by acid catalysed cyclisation gave the 6,6-spiroacetal 11-methyl-5-phenylsulphinyl-1,7-dioxaspiro[5.5] undecane. Alternatively, an `all intramolecular' process was developed whereby sequential base and acid catalysed cyclisation of the alcohol 8-[(tert-butyldimethyl)siloxy]-4-methyl-6-phenylsulphinyl-4,5-octadien-1-ol led to the formation of the 6,5-spiroacetal 10-methyl-4-phenylsulphinyl-1,6-dioxaspiro[4.5]decane. In chapter four, acid catalysed cyclisation of the allenyl sulphide 5-methyl-3-phenylsulphenyl-3,4-hexadien-1-ol gave the simple dihydropyran 2,2-dimethyl-4-phenylsulphenyl-5,6-dihydropyran but the corresponding allenyl sulphoxide, 5-methyl-3-phenylsulphinyl-3,4-hexadien-1-ol, did not cyclise under the same conditions. In complete contrast, the successful acid catalysed cyclisation of the diol 5-methyl-3-phenylsulphinyl-3,4-octadien-1,8-diol giving the dihydropyran 2-(3-hydroxypropyl)-2-methyl-4-phenylsulphinyl-5,6-dihydropyran is thought to be due to the presence of an extra hydroxyl group. A base catalysed 1,4-addition then gave the 1,5-dioxadecalin perhydro-8a-methyl-4-(phenylsulphinyl)pyrano[3,2-b] pyran. Overall, the sequence of acid and base or base and acid catalysed cyclisations allows the construction of both spiroacetals and 1,5-dioxadecalins from a similarly functionalised allenyl sulphoxide precursor.
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