Nuclear Magnetic Resonance Studies. XXVII. Homoenolization of Fenchone. A Mechanistic Study Utilizing C And H Nuclear Magnetic Resonance

1975 ◽  
Vol 53 (2) ◽  
pp. 212-223 ◽  
Author(s):  
A. L. Johnson ◽  
J. B. Stothers ◽  
C. T. Tan
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Deuterium Exchange ◽  
Mechanistic Study ◽  
Deuterium Incorporation ◽  
Magnetic Resonance Studies ◽  
Exchange Processes ◽  
Nuclear Magnetic

Deuterium exchange occurs at five β positions in fenchone under homoenolization conditions (t-BuO−–t-BuOD, 185°), C-6(exo and endo), C-8, C-9, and C-10. Both13C and 2H n.m.r. methods were employed to monitor deuterium incorporation and the particular advantages of the latter are illustrated. The relative rates of the five exchange processes were determined directly by 2H n.m.r. in contrast to the earlier homoenolization studies for which the stereoselectivity of exchange was established indirectly. The intermediate homoenolate ion can lead to rearrangement and the rearrangement products have been characterized by 13C n.m.r. as the 3,3,6-trimethyl-norcamphors. Homoenolization of this mixture gave further evidence on the stereochemistry of homoenolate formation.

Nuclear magnetic resonance studies. XL. Tricyclooctanone rearrangement, [3.2.1.0] → [3.3.0.0], via γ-enolization and a 2Hmr study of H/D exchange in tricyclic ketones

1984 ◽  
Vol 62 (7) ◽  
pp. 1385-1391 ◽  
Author(s):  
A. K. Cheng ◽  
Ashim K. Ghosh ◽  
J. B. Stothers
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Membered Ring ◽  
Deuterium Incorporation ◽  
Magnetic Resonance Studies ◽  
Endo Isomer ◽  
Exchange Processes ◽  
Initial Transformation ◽  
Nuclear Magnetic

The effect of strongly basic conditions (t-BuO−/t-BuOH/185 °C) on the exo and endo isomers of 7,7-dimethyltri-cyclo[3.2.1.02.4]octan-6-one has been examined. While the exo isomer is stable, the endo isomer readily rearranges to 4,4-dimethyltricyclo[3.3.0.02.8]octan-3-one (6) which subsequently undergoes reduction of the three-membered ring. The initial transformation is one of very few examples of γ-enolate rearrangement. Experiments in tert-buiyl alcohol-O-d1 were carried out to establish the several sites of deuterium incorporation in the initial ketones and in 6 using 2Hmr. These results reveal the stereochemistry of γ-enolate formation and cleavage as well as the stereoselectivities and relative rates of the exchange processes.

Nuclear magnetic resonance studies of ketone•BF3 complexes. II. The boron trifluoride catalyzed condensation of acetone

1968 ◽  
Vol 46 (24) ◽  
pp. 3799-3811 ◽  
Author(s):  
R. J. Gillespie ◽  
J. S. Hartman
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Boron Trifluoride ◽  
Methylene Chloride ◽  
Aldol Condensation ◽  
Condensation Reaction ◽  
Magnetic Resonance Studies ◽  
Exchange Processes ◽  
Donor Acceptor ◽  
Nuclear Magnetic

A detailed study of the reactions of the acetone•BF3 complex in excess acetone has been carried out by "F nuclear magnetic resonance (n.m.r.) spectroscopy. It is shown that rapid reversible fluorine exchange processes occur in solution, in addition to the slower aldol condensation–dehydration reaction. Two of the new 19F absorptions which appear during the reaction are shown to arise from BF3 complexes of donors which are formed by condensation and dehydration of acetone. The rate of the aldol condensation reaction is shown to fall off markedly as an increasing proportion of the BF3 becomes complexed with water; thus BF3 catalysis of the reaction appears to depend on the existence of a ketone–BF3 donor–acceptor bond. 1H and 19F n.m.r. studies of the acetone•BF3 complex in methylene chloride throw some light on the apparent greatly decreased reactivity of the complex in this solvent. Evidence is presented for the reversibility of the first step of the condensation reaction.

13C nuclear magnetic resonance studies. 114. An examination of the [3.3.1.0] → [4.3.0.0] rearrangement via β-enolization and H/D exchange in tricyclic ketones

1985 ◽  
Vol 63 (6) ◽  
pp. 1250-1257 ◽  
Author(s):  
Arthur J. Ragauskas ◽  
J. B. Stothers
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Ring Expansion ◽  
Butyl Alcohol ◽  
Deuterium Incorporation ◽  
Magnetic Resonance Studies ◽  
Endo Isomer ◽  
Exchange Processes ◽  
Tert Butyl Alcohol ◽  
13C Nuclear Magnetic Resonance

The behavior of the exo and endo isomers of 7,7-dimethyltricyclo[3.3.1.02,4]nonan-6-one (5, 6) under strongly basic conditions (t-BuOH/t-BuOH/185 °C) has been examined. In sharp contrast to their [3.2.1.02,4] analogs, the endo isomer is stable while the exo readily rearranges to 8,8-dimethyltricyclo-[4.3.0.02,4]nonan-7-one (16). Experiments were carried out in tert-butyl alcohol-O-d1 to establish the sites of deuterium incorporation in the initial ketones as well as the relative rates and stereoselectivities of the exchange processes. Ketones 5 and 6 were prepared through ring expansion by ketonization of cyclopropoxides generated from the [3.2.1.0] homologs; the stereochemistry of these ketonizations was established by 2H labelling.

Nuclear magnetic resonance studies. XXXI. Rearrangement and deuterium exchange through β-enolization in bicyclooctanones. An 2H nuclear magnetic resonance study.

1977 ◽  
Vol 55 (3) ◽  
pp. 447-453 ◽  
Author(s):  
A. K. Cheng ◽  
J. B. Stothers ◽  
C. T. Tan
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Nuclear Magnetic Resonance Study ◽  
Magnetic Resonance Study ◽  
Deuterium Incorporation ◽  
Proton Abstraction ◽  
Magnetic Resonance Studies ◽  
H Nmr ◽  
Derivatives Of ◽  
Nuclear Magnetic

The bicyclo[2.2.2]octan-2-one and -[3.2.1]octan-6-one skeletons are interconvertible under strongly basic conditions. Their α,α-dimethyl derivatives in tert-Buo−/tert-BuOH at 185 °C undergo very slow interconversion by β-proton abstraction. Using 2H nmr the stereoselectivity of deuterium incorporation at the β-methylene sites was established. The relative reactivities of β-methyl exchange in the [3.2.1] system were also determined. As models for this process, exchange in the α,α,α′,α′-tetramethyl derivatives of the monocyclic ketones, C5–C8, was also studied.

scholarly journals Nuclear magnetic resonance studies. XXX.Hydrogen–deuterium exchange in bicyclo[3.2.1] and -[2.2.2]octenes through allylic and vinylic anions

1977 ◽  
Vol 55 (1) ◽  
pp. 50-55 ◽  
Author(s):  
A. K. Cheng ◽  
J. B. Stothers
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Deuterium Exchange ◽  
Hydrogen Deuterium Exchange ◽  
Magnetic Resonance Studies ◽  
H Nmr ◽  
Hydrogen Deuterium ◽  
Nuclear Magnetic

Bicyclo[3.2.1]oct-2-ene undergoes hydrogen–deuterium exchange through allyl and vinyl carbanionic intermediates under strongly basic conditions, tert-BuO−/tert-BuOD) at 185 °C. Only allylic exchange had been observed in previous studies with tert-BuO−/DMSO. Since the 2-tert-butoxybicyclo[3.2.1]octanes are stable under these conditions an addition–elimination sequence cannot account for exchange at C-3. The relative rates of exchange at C-2, -3, and -4, and the stereoselectivity at the allylic site were determined by 2H nmr. For comparison, the rate of olefinic exchange in bicyclo[2.2.2]octene was also measured.

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