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Part I, a photoprecursor for difluorocarbene: Part II, syntheses and studies of the highly fluorinated [2.2.2] propellanes.

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Call No.	QD305.H15 H4 2003
Author	He, Yigang, 1973-
Title	Part I, a photoprecursor for difluorocarbene: Part II, syntheses and studies of the highly fluorinated [2.2.2] propellanes.
Date	2003
Abstract	Part I. A photoprecursor for difluorocarbene. The goal of this research was to develop a more practical and efficient photoprecursor for difluorocarbene. The first approach was concerned with the synthesis of 4,4-difluoropyrazoline-3,5-dione ( 5 ). We were able to synthesize 4,4-difluoropyrazolidine-3,5-dione ( 7 ) by a short and efficient route, but the oxidation of 7 was unsuccessful. Pyrazoline 5 was found to be an extremely labile compound and unsuitable for our original purpose to use it as a photoprecursor for difluorocarbene. Our second target, 10,10-difluorobicyclo[4.3.1]deca-1,3,5-triene ( 31 ), was synthesized in an overall yield of 55% from indan, and no chromatography was required. This triene was found to be a practical source of difluorocarbene for photochemical as well as thermal cyclopropanation reactions. Part II. Syntheses and studies of the highly fluorinated [ 2.2.2 ] propellanes. Synthesis of 4,4-dibromooctafluorobicyclo[2.2.0]hexane ( 33 ), a bottleneck on the route to fluorinated [2.2.2]propellanes, was greatly improved. Reduction of 33 using 20 equivalents of activated zinc yielded the highly strained olefin, octafluorobicyclo[2.2.0]hex-1(4)ene ( 45 ), which was trapped by 10 equivalents of ethyl vinyl ether in situ to yield the highly fluorinated [2.2.2]propellane 35 in an isolated yield of 77%. The reactions of 35 with tetrabutylammonium halides were also greatly improved in yields. The half-life of 35 was measured to be 40.1 h at 21°C using 1 H NMR. Olefin 45 reacted with dimethylketene to give us a second highly fluorinated [2.2.2]propellane, 49. This propellane showed striking stability as compared with 35 , presumably because of the stronger electron withdrawing capability of the carbonyl relative to the ethoxy group. Even more stable [2.2.2]propellane 58 was obtained in a quantitative yield by the [2+2]cycloaddition of 45 to 2-difluoromethylene-1,3-dioxolane ( 57 ). Propellane 58 shows amazing stability and very different reactivity from propellane 35. Propellane 58 is a strong oxidant and is reduced by halides to form 59. Methyl iodide can be added regioselectively across the central bond in one direction via an ionic chain and in the other via a radical chain pathway. Protic solvents and electrophiles attack the C1-C2 bond, but not the central bond, to form orthoester 69 , hydroxyester 71 and bromoester 73. When there is no proton source and methyl iodide in the reaction system, oligomerization of 58 occurs. Olefin 45 was found to be very stable thermally. It can react with ethyl formate in a radical fashion to form ester 78. Olefin 45 also reacted with 1,3-cyclohexadiene to form 87 and 88 through ene and [2+4]cycloaddition mechanisms respectively. The latter was hydrogenated to give the highly symmetric 91. Olefin 45 is an incredible dienophile; it reacts with naphthalene, durene even benzene to give the Diels-Alder adducts 97 , 99 and 102.
Description	xvii, 167 leaves : ill. 28 cm.
Format	application/pdf
Advisor	David M. Lemal
Subject	Organofluorine compounds -- Synthesis. Carbenes (Methylene compounds) -- Synthesis. Propellanes -- Synthesis.
College	Dartmouth College -- Department of Chemistry.
Issuing Body	Dartmouth Dissertations are made available through the Dartmouth Digital Library.
Degree	Thesis (Ph.D.)--Dartmouth College.
Copyright	All rights reserved. No part of this book may be reproduced in any form by any electronic or mechanical means without permission in writing from the author.
DOI	http://dx.doi.org/10.1349/ddlp.13

Title	Page 1
Format	application/pdf
Issuing Body	Dartmouth Dissertations are made available through the Dartmouth Digital Library.
Degree	Thesis (Ph.D.)--Dartmouth College.
Full Text	Dr. Carol L. Foit Part I A Photoprecursor for Difluorocarbene Part II Syntheses and Studies of the Highly Fluorinated [2.2.2]Propellanes A Thesis Submitted to the Faculty in partial fulfillment of the requirements for the degree of Doctor of Philosophy In Chemistry by Yigang He DARTMOUTH COLLEGE Hanover, New Hampshire March 24, 2003 Examining Committee: Dr. Davi<l)M. Lemal" Dr. Peter A. Jacobi Dr. Charles~ B. racun.Y _ <~ fir. Glen P. Miller Dean of Graduate Studies

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