Cyclizations and substitutions of unsaturated sulfur compounds

The first chapter of this thesis includes an exploration of the breadth and mechanism of a novel base-induced cyclization reaction. Treatment of benzyl propargyl sulfides with two equivalents of KO tBu in CH3CN at room temperature or reflux gives access to 2-aryl-2,3-dihydrothiophenes in yields ranging from 10-74%. It has been determined that an aryl ring bearing substrates that possess some electronegative character or some electronegative constituent atoms and are mild pi- or sigma- electron acceptors are essential for efficient cyclization. Substitution may be at the ortho, meta, or para position of the aryl ring. In addition, a select number of dihydrithiophenes were successfully oxidized to the corresponding thiophenes through the use of DDQ in CHCl 3 at 25°C.;The second chapter of this thesis explores the chemistry of alpha,beta-unsaturated sulfoxides and sulfinate esters. A study was done to examine the regioselectivity of the ring opening of styrene oxide by thiolates with the aim of preparing 2-phenylethenyl sulfoxides. The results indicate that although the ratio of regioisomers is high, yields for the reactions are unspectacular. Subsequently, a family of optically enriched 2-phenylethenyl sulfoxides were prepared through Grignard reactions of diastereomerically pure 2-phenylethenyl cholesteryl sulfinates. Yields from 70-87% were found with ee's ranging from 91-97%.;Finally, an "atypical" chiral alcohol was explored for the preparation of optically enriched alpha,beta-unsaturated sulfinate esters. Both yield and de's of the sulfinates were comparable to or higher than those found using cholesterol and in some cases the isolated sulfinate esters were solids, however, the alcohol was found to be incompatible with sulfinyl chlorides bearing Michael acceptors on the beta-carbon of the alkene.;The proposed mechanism of the reaction includes an isomerization of the propynyl group to the allenyl or propargyl isomer. In order to investigate the mechanism of the reaction, a number of compounds were synthesized which would prevent isomerization of the propynyl side chain. In addition, exploration into a possible 2,3-sigmatropic rearrangement followed by ring closing was explored. Successful cyclization of these examples show that any of the proposed mechanisms are feasible for the cyclization reaction. Finally, an NMR study of proton/deuterium exchange in the substrates was undertaken. The results indicate that deprotonation and deuterium exchange at the benzyl position occurs fastest, and exchange at the benzyl and propynyl units are complete prior to appearance of cyclized product.