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Title: Synthesis and application of chiral sulfides in asymmetric cyclopropanation and epoxidation reactions
Author: Saha, Chandreyee
ISNI:       0000 0004 2737 0140
Awarding Body: University of Bristol
Current Institution: University of Bristol
Date of Award: 2012
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Application of two different chiral sulfides m asymmetric cyclopropanation and epoxidation reactions have been studied. Cyclopropanation reactions of chiral stabilised sulfonium ylides derived from chiral sulfide 13 with acyclic enones have been studied. The surprisingly low enantioselectivity obtained in such reactions was proposed to be due to a rapid and reversible intramolecular proton transfer process occurring within the betaine intermediate prior to ring-closure. The hypothesis was verified by carrying out the reactions of stabilised sulfonium ylides with methyl vinyl ketone. Variation in enantioselectivities were observed when the ylide substituent was varied from ketone to ester to amide. Isotope effects were also studied to further support the hypothesis. Improvement in enantioselectivities were observed in deuterium incorporated cyclopropanes. The study was further extended to ammonium ylide cyclopropanation reactions to study the cause of erosion in enantioselectivity in certain ammonium ylide- mediated cyclopropanation reactions. Chiral sulfide isothiocineole 59, has been recently reported by the Aggarwal group. The sulfide was easily prepared in one step from limonene 75 and y-terpinene 76 although in low yield. The one-step reaction was investigated further. Stoichiometry, time and order of addition of reagents were varied and a substantial improvement in the synthesis of 59 was achieved. Isothiocineole 59 was applied in asymmetric epoxidation reactions and the scope of ylide reactions in terms of ylide substituents (aryl, alkenyl) and aldehydes (aromatic and aliphatic) was explored.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available