This critical review, which is relevant to researchers in synthetic organic chemistry, focuses on asymmetric 1,3-dipolar cycloadditions with acrylamides. The use of chiral acrylamides as dipolarophiles leads to high levels of stereocontrol, due to conformational constraint in the acrylamides. Employment of chiral tertiary acrylamides containing nitrogen heterocycles is particularly effective in controlling the stereoselectivity. Following a general overview of 1,3-dipolar cycloadditions, the main body of the review focuses on asymmetric 1,3-dipolar cycloadditions of acrylamides with nitrile oxides, nitrones, diazoalkanes and azomethine ylides, with particular emphasis on the rationale for the observed stereocontrol (215 references).

Asymmetric 1,3-dipolar cycloadditions of acrylamides

4.04 – Pyrazoles and their Benzo Derivatives

A theoretical treatment of long‐range proton spin—spin coupling constants, 4JHH′, across four bonds in saturated and unsaturated hydrocarbons is presented. Using the valence bond formalism, explicit theoretical expressions for the `direct'' and ``indirect'' contributions to 4JHH′ are obtained. By introducing a semiempirical criterion for estimating the pertinent exchange integrals, the angular dependence of the ``indirect'' effect is evaluated. The calculated results correlate a wide range of coupling‐constant data including those experimental results for which existing theoretical treatments are inadequate. The comparison of the calculated with the experimental data suggests that the ``direct'' contribution to long‐range coupling constants in saturated systems is negative in sign and is most important in the vicinity of the eclipsed conformations.

Angular Dependence of Long‐Range Proton Coupling Constants Across Four Bonds

Thermische Cyclisierungen von Dienen, Eninen, Enonen und ahnlichen ungesattigten Systemen illustrieren das praparative Potential der intramolekularen En-Reaktion. Eine Fulle substituierter, anellierter und uberbruckter Ringsysteme, darunter auch Naturstoffe, sind so auf regio- und stereoselektive Weise zuganglich. Zahlreiche Beispiele dienen dazu, die Moglichkeiten, Grenzen und gemeinsamen Gesetzmasigkeiten dieser Cyclisierungs- und der dazu inversen Ringoffnungs-Reaktion zu umreisen. Manche dieser Cyclisierungen sind in industrieller Grosenordnung durchfuhrbar.

Intramolekulare En‐Reaktionen in der organischen Synthese

1. The metabolism of (+)-citronellal, (+-)-7-hydroxycitronellal, citral, (-)-perillaldehyde, (-)-myrtenal, cuminaldehyde, thujone, and (+-)-carvone was studied in rabbits. 2. In (+-)-7-hydroxycitronellal, (-)-perillaldehyde, (-)-myrtenal and cuminaldehydes, both primary alcohols and carboxylic acids were formed. 3. In (-)-citronellal and citral, regioselective oxidation was found and a trans-positioned methyl group was carboxylated in each case. 4. In o-cuminaldehyde, reduction but not oxidation, was found.

Terpenoid biotransformation in mammals. V. Metabolism of (+)-citronellal, (+-)-7-hydroxycitronellal, citral, (-)-perillaldehyde, (-)-myrtenal, cuminaldehyde, thujone, and (+-)-carvone in rabbits.

The results of analysis of methyl citraconate and mesaconate, methyl cis- and trans-crotonate, and methyl cis- and trans-2-pentenoate are reported. A previously reported analysis of the crotonates by first-order perturbation theory gave significantly different values for the 1,3 coupling constants. The discrepancy in results, which is due to the importance of second-order effects, emphasizes the need for caution in applying the first-order method. From values of 1,3 coupling constants reported here and elsewhere it is concluded that there is no simple relation between the magnitude of 1,3 coupling constants and geometrical configuration of the interacting nuclei.

N.M.R. SPECTRA OF SOME α–β UNSATURATED ESTERS

cis- and trans-3.5-Dimethyl-3-carbomethoxy-Δ1-pyrazoline (IV and V) have been separated, and product analysis for the pyrolysis and photolysis of these compounds has been completed. The cyclopropan...

Pyrazolines: vi. the stereochemistry in the pyrolysis of pyrazolines for the c3 and c5 positions of the pyrazoline molecule

The geometrically isomeric cis- and trans-5-3-methyl-4-ethyl-3-carbomethoxy-Δ1-pyrazolines were prepared and their pyrolysis and photolysis studied. The isomeric pyrazolines gave cyclopropane products of mixed stereochemistry, but predominantly with retention of the stereochemistry present in the starting pyrazoline. Each pyrazoline gave stereospecifically a different α,β-unsaturated ester product. This stereospecificity can be related to the structure of the pyrazoline through the requirement that the loss of nitrogen must be from the side of the pyrazoline that is trans to the hydrogen at C-4.

Pyrazolines. VII. Concerning the formation of olefins from the pyrolysis of pyrazolines

The thermal and photochemical conversion of (1R*,2R*,3S*), (1S*,2R*,3S*), and (1S*,2R*,3R*)-1-acetyl-1,2-dimethyl-3-phenylcyclopropane (1, 2, and 3) to cis- and trans-2,3,4-trimethyl-5-phenyl-4,5-d...

A Stereochemical and Kinetic Study of the Conversion of Methyl Cyclopropyl Ketones to 4,5-Dihydrofurans

Methyl cis-4-methyl-2-pentenoate (1) has been found to rearrange at 252 °C by a simple first-order and presumably unimolecular mechanism to methyl 4-methyl-3-pentenoate (3) with a rate constant k o...

Donald E. McGreer

Papers

N.M.R. SPECTRA OF SOME α–β UNSATURATED ESTERS

Pyrazolines: vi. the stereochemistry in the pyrolysis of pyrazolines for the c3 and c5 positions of the pyrazoline molecule

Pyrazolines. VII. Concerning the formation of olefins from the pyrolysis of pyrazolines

A Stereochemical and Kinetic Study of the Conversion of Methyl Cyclopropyl Ketones to 4,5-Dihydrofurans

Thermal rearrangement of α,β- to β,γ-unsaturated esters. Evidence for a 1,5-hydrogen transfer mechanism