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Title:Radical rearrangement in the spiro(cyclopropane-1,1'-indan) and 3',4'-dihydrospiro(cyclopropane-1,1'(2H)-naphthalene) systems. An investigation of fast radical clocks
Author(s):Lemieux, Robert Philippe
Doctoral Committee Chair(s):Beak, Peter
Department / Program:Chemistry
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Chemistry, Organic
Abstract:The ring opening rearrangements of cyclopropylcarbinyl radicals incorporated in rigid indanyl and tetrahydronaphthyl frameworks were investigated by the competitive tin hydride method. At 75$\sp\circ$C, the spiro (cyclopropane-1,1$\sp\prime$-indan) -2$\sp\prime$-yl and 3$\sp\prime$,4$\sp\prime$-dihydrospiro (cyclopropane-1,1$\sp\prime$(2$H$)-naphthalene) -2$\sp\prime$-yl radicals undergo ring opening with rate constants of 2.11 $\times$ 10$\sp9$ s$\sp{-1}$ and 2.99 $\times$ 10$\sp9$ s$\sp{-1}$, respectively. The 3$\sp\prime$,3$\sp\prime$-dimethylspiro (cyclopropane-1,1$\sp\prime$-indan) -2$\sp\prime$-yl and 3$\sp\prime$,4$\sp\prime$-dihydro-3$\sp\prime$,3$\sp\prime$-dimethylspiro (cyclopropane-1,1$\sp\prime$(2$H$)-naphthalene) -2$\sp\prime$-yl radicals undergo ring opening with rate constants of 8.53 $\times$ 10$\sp9$ s$\sp{-1}$ and 3.51 $\times$ 10$\sp9$ s$\sp{-1}$, respectively. Dispiro (cyclopropane-1,1$\sp\prime$-indan-3$\sp\prime$,1$\sp{\prime\prime}$-cyclopropane) -2$\sp\prime$-yl radical undergoes ring opening with a rate constant of 5.2 $\times$ 10$\sp8$ x$\sp{-1}$. The rate enhancement observed in the rearrangement of the spiroindanyl and spirotetrahydronaphthyl radicals relative to that of the acyclic cyclopropylmethyl radical ($k\sb{\rm r}$ = 5.21 $\times$ 10$\sp8$ s$\sp{-1}$ at 75$\sp\circ$C) is rationalized in terms of (a) favorable overlap of the reacting orbitals held in a rigid conformation, (b) greater relief of ring strain in the transition state, and (c) stabilization of the developing double bond in the transition state by the adjacent phenyl ring. Semiempirical AM1 and MNDO calculations failed to provide a reasonable correlation with these experimental results. Attempts to evaluate the effect of cyclopropane methyl substituents on the rate of rearrangement of spiroindanyl radicals by an intramolecular competition experiment were unsuccessful, due to the instability of the required radical precursors.
Dispiro (cyclopropane-1,1$\sp\prime$-indan-3$\sp\prime$,1$\sp{\prime\prime}$-cyclopropane) -2$\sp\prime$-one undergoes Wolff-Kisner reduction with loss of a cyclopropane ring. This heretofore unreported "ethylene extrusion"reaction occurs prior to treatment with base to afford a spiroindanone hydrazone intermediate. The mechanism proposed for this transformation involves the initial formation of a dispiroindanone hydrazone intermediate, which is converted to a fused pyrazoline intermediate via a $\pi$2s + $\pi$2s + $\omega$2s electrocyclic ring closure. This intermediate reacts with hydrazine, with subsequent loss of diimide and ethylene to afford the spiroindanone hydrazone that subsequently reacts with base to afford the reduced product. Results from product studies and $\sp1$H NMR and GC/MS time-dependent studies are consistent with the proposed mechanism.
Issue Date:1989
Rights Information:Copyright 1989 Lemieux, Robert Philippe
Date Available in IDEALS:2011-05-07
Identifier in Online Catalog:AAI9010930
OCLC Identifier:(UMI)AAI9010930

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