Phyllis A. Leber

Molecular rearrangements through thermal [1,3] carbon shifts

Molecular rearrangements through thermal [1,3] carbon shifts, such as vinylcyclopropane-to-cyclopentene and vinylcyclobutane-to-cyclohexene isomerizations, were recognized and exemplified repeatedly from 1960-1964. Serious mechanistic studies of these and related rearrangements over the past 40 years have provided ample grounds for interpreting them as processes taking place by way of conformationally flexible but not statistically equilibrated diradical intermediates. Orbital symmetry theory fails to account for the stereochemical characteristics of [1,3] carbon shifts. For sigmatropic reactions of this class the theory can no longer be retained as a valid basis for mechanistic interpretations, or even as a serious contender for consideration as a mechanistic possibility.

Preparation of 7-Methyl-7-vinylbicyclo[3.2.0]hept-2-ene Via Cyclobutanone Reduction

Abstract A cyclobutanone to cyclobutane conversion has been performed on 7-methyl-7-vinylbicyclo[3.2.0]hept-2-en-6-one by low-temperature (25°C) Wolff-Kishner reduction of the hydrazone derivative. Upon heating, the exo-vinyl epimer affords predominantly cis-6-methyl-4,7,8,9-tetrahydroindene.

Choline conjugates of auxins. I. Direct evidence for the hydrolysis of choline-auxin conjugates by pea cholinesterase

We synthesized the choline conjugates of three derivatives of phenylacetic acid, four derivatives of phenoxyacetic acid, and of naphthalene-1-acetic acid and measured the effects of these conjugates on pea (Pisum sativum L. cv. Alaska) stem segment elongation. We also synthesized the thioester analogs of six choline conjugates and measured their rates of hydrolysis by pea cholinesterase and their rates of spontaneous hydrolysis. With one exception, conjugates that stimulated growth were hydrolyzed at high rates by pea cholinesterase, while conjugates that were hydrolyzed at low rates by pea cholinesterase did not stimulate growth. The results are consistent with a model in which cholinesterase releases active auxins from these conjugates.

The thermal rearrangement of 7,7-dimethylbicyclo[3.2.0]hept-2-ene

Abstract The title compound, when subjected to gas-phase pyrolysis at 275°C, undergoes predominantly fragmentation to cyclopentadiene and isobutylene.

Thermal reactions of endo- and exo-6-methylbicyclo[3.2.0]hept-2-enes: an experimental test for a potential ring inversion

Abstract endo -6-Methylbicyclo[3.2.0]hept-2-ene at 275°C in the gas phase isomerizes and fragments with a first-order rate constant for disappearance of 7.3×10 −6 s −1 . The exo -methyl isomer is not formed; the ring inversion isomerization of the bicyclo[3.2.0]hept-2-ene is not kinetically competitive.

The Thermal Rearrangement of Endo-7-Methyl-exo-7-vinylbicyclo[3.2.0]Hept-2-ene

Abstract Gas-phase thermolysis of the title compound in the temperature range of 150°–166°C yields predominantly cis -6-methyl-4,7,8,9-tetrahydroindene by tandem [1,3]–[3,3) sigmatropic shifts: however, we cannot exclude some direct conversion by an alternative [1,3] sigmatropic migration.

A versatile and efficient methodology for the preparation of choline ester auxin conjugates

Abstract A two-step synthetic strategy affords indole-3-acetylcholine (IAC) from indole-3-acetic acid (IAA) via the intermediacy of 2-dimethylaminoethyl indole-3-acetate. Thus, treatment of indole-3-acetate with 1-dimethylamino-2-chloroethane, followed by methylation with methyl iodide, yields 55–70% recrystallized IAC from IAA. Using the same methodology, six analogues of IAC have been prepared in overall yields ranging from 40 to 60%.

The thermal rearrangement of 6-methyl-6-vinylbicyclo)[3.2.0]heptane

Abstract Gas-phase pyrolysis of the endo -vinyl epimer (1 A ) of the title compound at 275°C affords predominantly 3-(2-methyl-2-butenyl)cyclopentene (presumably the Z isomer), a direct [1,5]-hydrogen shift product, whereas the exo -vinyl epimer (1 B ) favors the fragmentation products, cyclopentene and isoprene.

Thermal Isomerizations of cis,anti,cis-Tricyclo[7.4.0.02,8]tridec-10-ene

cis,anti,cis-Tricyclo[7.4.0.0(2,8)]tridec-10-ene (13TCT) undergoes [1,3] sigmatropic rearrangements at 315 °C in the gas phase to the si product 1 and to the sr product 2 with si/sr = 2.1. The dominant thermal isomerization process, however, is epimerization at C8 to afford product 3. That stereomutation at C8 occurs 50% faster than the si and sr shifts combined.

A Diastereoselective Preparation of 7-Ethyl-7-methylbicyclo[3.2.0]HEPT-2-en-6-one(1)

Abstract Alkylation of 7-endo-ethylbicyclo[3.2.0]hept-2-en-6-one (2a) and 7-endo-methylbicyclo[3.2.0]hept-2-en-6-one (2b) with lithium diisopropylamide (LDA) and the appropriate alkyl iodide (methyl and ethyl iodide, respectively) afforded the title compound such that alkylation had occurred exclusively on the exo face of the bicyclo[3.2.0] system.