Induced Ionization in 1,4-Diol Monosuylfonate Esters and its Application in the Synthesis of Natural Products

Abstract

The chemical manifestations of orbital interactions through four σ-bonds in the base-induced and -directed reactions of monosulfonated trans-perhydronaphthalene- and norbornane-1,4-diols are discussed. Through-bond interactions (TBI) and σ-participation are the most important stereoelectronic effects which principally determine their reactivity. Dependent on the geometry of the relaying C-C bonds, these compounds react by three chief pathways: rearrangement, elimination, and homofragmentation. Substituents at carbon atoms adjacent to the carbon atom bearing the sulfonate ester group increase the contribution of σ-participation, which is expressed in a higher reactivity of these compounds. In cases where the ideal W arrangement is not distorted by alkyl substituents, the co-operation of TBI and σ-participation results in a fast homofragmentation. Through-space interactions (TSI), if occurring next to TBI, have only a modest influence on the reactivity of these compounds. Secondary monosulfonate esters of rigid 1,4-diols do show these typical reactions after induced ionization but the ionization of primary sulfonate esters can not be induced in a similar way. The results obtained from the reactions on monomesylated cholestane-3,7-diols, as model systems for cyclic 1,5-diol monosulfonate esters, show that chemical consequences of TBI and σ-participation still can be observed in these systems, but play only a minor role in their reaction patterns. Applications of reaction strategies in which orbital interactions through four σ-bonds play an essential role are demonstrated in the total syntheses of cis-fused guaiane sesquiterpenes, alloaromadendrenes, α- santalanes and marasmanes.