Pyrazolines. VIII. The Syntheses of 5,5-Diaryl-2-pyrazolines from the Reaction of Diazoalkanes with Methyl Acrylate¹

Stereocontrol of intramolecular Diels–Alder reactions by an allylic diphenylcyclopropyl group

“…Oxidation of benzophenone hydrazone 8 22 with nickel peroxide gave diphenyl diazomethane 9, 23 which underwent cycloaddition with methyl acrylate at room temperature 24 to afford cyclopropane ester 10. 25 Reduction to primary alcohol 11 with lithium aluminium hydride followed by Swern oxidation afforded aldehyde 12 in 75% yield over 4 steps.…”

“…in petroleum spirit (20 mL) at rt afforded the cyclopropane ester 10. 24 No purification was necessary in this three step preparation. Compound 4, 145.0, 140.5, 129.8, 128.7, 128.6, 127.8, 127.3, 126.8, 52.0, 40.2, 29.1, 20.4 A solution of compound 10 (0.26 g, 1.02 mmol, 1 equiv.)…”

Diphenyldiazomethane

“…In the presence of a trace of acid the pyrazolines so obtained spontaneously undergo loss of N 2 to provide the corresponding cyclopropane. 12 This reaction is so sensitive to acid that base-washed glassware must be used in order to isolate the pyrazoline with certain substrates such as methyl Avoid Skin Contact with All Reagents acrylate (eq 5). If no acid is present, or if a mild base such as Triethylamine is added, then the pyrazolines must be heated in order to extrude N 2 .…”

Synthesis of 2‐pyrazolines by the reactions of α,β‐unsaturated aldehydes, ketones, and esters with diazoalkanes, nitrile imines, and hydrazines

“…5-Substituted and 4,5-disubstituted 2-pyrazoline-3-carboxylic acid esters 6 have been synthesized by the reaction of α,β-unsaturated carboxylic acid esters 3 with substituted diazomethanes 5 (Scheme 2) [4,10,23]. 5,5-Diphenyl-3-(methoxycarbonyl)-2-pyrazo-line (8) has been synthesized by a base-catalyzed isomerization of 1-pyrazoline 7 obtained as a primary product of the cycloaddition of methyl acrylate with diphenyldiazomethane (Scheme 2) [24].…”

“…Thermal denitrogenation of the pyrazoline carboxylic acid derivatives affording cyclopropanes has also been thoroughly investigated by several research groups [10,13,23,24]. This reaction proved to be a simple and convenient procedure for the preparation of cyclopropane derivatives.…”