Dimetization kinetics and products of. alpha. -substituted o-quinodimethanes derivd from benzene and furan
a-Substituent effects on the dimerization of furan-based and benzene-based o-quinodimethanes (o-QDM's) are reported. The mechanistic implications of these results are discussed. 3-Ethylidene-2-methylene-, 2-ethylidene-3-methylene-, and 2,3-diethylidene-2,3-dihydrofuran were prepared by fluoride induced 1,4-conjugative elimination of trimethylsilyl acetate from the appropriate precursors. The {sup 1}H NMR spectra of these furan-based o-quinodimethanes were obtained and the dimerization products of each were studied. It was found that a methyl group at the 3-methylene position retards the rate of of dimerization which is consistent with the previously proposed dimerization mechanism, the two-step diradical mechanism. The preparation of a-methyl-, a-cyclopropyl-, a-tert-butyl-, and a-mesityl-o-oxylylene and the kinetics and product analyses of their Diels-Alder reactions and dimerization are reported. Trapping the reactive o-QDM's with methyl methacrylate gives more of the ortho'' than the meta'' isomers in all cases we studied. The change from a-methyl- to a-cyclopropyl to a-tert-butyl-o-xylylene results in a decrease of the ortho'' to meta'' ratio from 8.8 to 4.3 to 2.2, respectively. The trend of the regioselectivity is consistent with the concerted mechanism. 35 refs., 92 figs., 65 tabs.
- Research Organization:
- Ames Lab., IA (United States)
- Sponsoring Organization:
- DOE; USDOE, Washington, DC (United States)
- DOE Contract Number:
- W-7405-ENG-82
- OSTI ID:
- 5236904
- Report Number(s):
- IS-T-1567; ON: DE91018555
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
400201* -- Chemical & Physicochemical Properties
AROMATICS
BARYONS
BENZENE
CHEMICAL PREPARATION
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
DIENES
DIMERIZATION
ELEMENTARY PARTICLES
FERMIONS
FURANS
HADRONS
HETEROCYCLIC COMPOUNDS
HYDROCARBONS
KINETICS
NMR SPECTRA
NUCLEONS
ORGANIC COMPOUNDS
ORGANIC OXYGEN COMPOUNDS
POLYENES
POLYMERIZATION
PROTONS
RADICALS
REACTION KINETICS
SPECTRA
SYNTHESIS