Synthesis and chemistry of 1,4-oxathianes and 1,4-oxathian-3-ones
The exploration of possible routes towards the synthesis of alkylated oxathiane and oxathianone systems are presented in this research thesis. The ultimate objective of these studies was the synthesis of dihydrofurans and dihydrofuranones via the Ramberg-Bäcklund rearrangement. Initially, studies were carried out on the alkylation of the cyclic ether, 1,4-oxathiane S.S-dioxide. It was during investigations with the readily available cyclic ether that several ring-opened novel compounds were synthesised. Subsequently, an alkylated epoxide was prepared and two pathways from this epoxide to the synthesis of an alkylated 1,4-oxathiane S.S-dioxide were examined. The first involved an examination influencing the regioselectivity of the epoxide and consequent ring-opening to yield the corresponding hydroxy sulfide. Further studies explored the possibility of either ring closure of the sulfide followed by oxidation to the sulfone or oxidation to the sulfone followed by cyclization. However, these routes were to prove unsuccessful. The second pathway involved the use of a readily available epoxide for the afore mentioned cyclization/oxidations. The preparation of oxathianones was the second part of these studies and involved the synthesis of the lactone 1,4-oxathian-3-one S.S-dioxide again with the aim of alkylating this sulfone for use as the precursor required in the Ramberg-Bäcklund reaction. Investigations included acid/alcohol cyclizations and catalytic oligomerization/depolymerization methods. Another sequence of reactions available to us was the direct oxidation of a hydroxy diol and/or lactol oxidation to the lactone. However, it was during this research towards the synthesis of the sulfone lactone that four unexpected and novel compounds were synthesised. The latter part of our studies took us to the preparation of an alkylated oxotetrahydrothiophene S.S-dioxide with the intention of performing the Baeyer-Villiger oxidation to the requisite lactone. However, success came with the double alkylation of the system rather than the mono-alkylation.
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