Studies on a catalytic cadogan cyclization by PI̳I̳I̳/PV̳=O redox cycling
Name
1036988309-MIT.pdf
Description
Full printable version
Size
12.99 MB
Format
Adobe PDF
Checksum (MD5)
d617e8adb933fc4b8e0db151709c7e26
Author(s)
Harrison, Tyler S. (Tyler Steven)
Advisor(s)
Alexander T. Radosevich.
Date Issued
2018
Publisher
Massachusetts Institute of Technology
Abstract
Organophosphorus reagents offer potential for developing catalytic protocols by inclusion of a reductant such as hydrosilanes to (re)generate the chemically active phosphine in situ. In our research, we have successfully adapted this concept to the Cadogan reductive cyclization by using a strained 4-membered phosphetane precatalyst, which proved to be more competent than acyclic and 5-membered analogs for P(III)/P(V)=O redox cycling. A variety of substrates were found to successfully undergo catalytic Cadogan indazole cyclization. The mechanism of the cyclization has been expanded. The resting state of phosphorus was determined to be the P" phosphetane, and this phosphetane proved to be 8 times faster than the acyclic n-Bu₃P at driving the reductive cyclization of N-phenyl o-nitrobenzaldimine to 2-phenylindazole. A nitrosoarene, presumed an intermediate in the overall cyclization, was found to undergo cyclization under reaction conditions. In addition, a new unique oxazaphosphetane was observed as an intermediate during the course of cyclization, which may lead to a more complete understanding of other-phosphorus mediated deoxygenations, including nitro reduction. Initial studies in nitro reduction have been undertaken, though further work is necessary to fully develop a phosphorus-mediated catalytic protocol.
Description
Thesis: S.M., Massachusetts Institute of Technology, Department of Chemistry, 2018.
Cataloged from PDF version of thesis. The double underlined I̳I̳I̳ and V̳ in title on title page appear as superscript capital letters.
Includes bibliographical references.
Subjects
Chemistry.
MIT Department
Massachusetts Institute of Technology. Department of Chemistry
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