Effect of substituents on the rate of pyramidal inversion of 1-aryl-2,2-dimethylaziridines

Abstract

This material did react with hydrazine to give an amino product (18) and subsequently a benzoyl derivative. However, neither of these has so far been purified or otherwise adequately characterized.«-Propyl 2-Thiazolothiazolecarbamate (19). To 2-thiazolothiazolecarbonyl hydrazide (12, 710 mg, 3.55 mmol) in 20 ml of aqueous hydrochloric acid, stirred with 400 ml of ether at 10°, was added 420 mg (5.9 mmol) of sodium nitrite. A precipitate of the azide was formed but was extracted by the ether as stirring was continued for 15 min. The ether phase and an ether extract of the aqueous phase was dried (magnesium sulfate and then Drierite) and then diluted with 100 ml of «-propyl alcohol. The ether was distilled and the alcohol solution was refluxed for 1 hr, concentrated to 10 ml, and allowed to stand at 20°. There was obtained 470 mg (55 %) of the «-propyl carbamate ( 19), mp 185-192°. The material was dissolved in ether, the solution was filtered and diluted with propyl alcohol, and the ether distilled to give colorless crystals, mp 192-194°. This process was repeated twice followed by sublimation (115-123°, 0.01 mm) for the analytical sample: mp 198-200.5°; uv Xmax 289 (log e = 4.22), 246 µ (log e = 3.78); ir Xmax

Rearrangement of N‐Aryl‐2‐Vinylaziridines to Benzoazepines and Dihydropyrroles: A Synthetic and Theoretical Study

“…However, since the barriers for configuration inversion experimentally [52,54] and theoretically [55,56] evaluated are below 30-35 kcal mol…”

“…Yield of Conformational analysis of N-aryl-2-vinylaziridines and rearrangement pathways: N-substituted aziridines are known to have a relatively large barrier to nitrogen inversion; [52,53] this gives rise to two distinguishable invertomers: one with the aryl substituent on the nitrogen atom cis to the vinyl group on the adjacent carbon atom, and another with a trans relationship between the two substituents (Scheme 2). However, since the barriers for configuration inversion experimentally [52,54] and theoretically [55,56] evaluated are below 30-35 kcal mol…”

Synthesis of Structurally Diverse 3-, 4-, 5-, and 6-Membered Heterocycles from Diisopropyl Iminomalonates and SoftC-Nucleophiles

“…In principle, two isomers are possible: the phenyl group can be cis or trans to the aziridine ring methine proton. If both isomers are present and inversion about the nitrogen is very fast, just one set of signals (representing the average environment) will be present, as is observed with N-( p -methoxyphenyl)-2,2-dimethylaziridine above the coalescence temperature T c of −26 °C . In general, conjugation of the nitrogen lone pair with an aromatic ring system is known to decrease the barrier to inversion about nitrogen. − The electron-donating nature of the p -methoxy substituent (present in 33b ) raises the barrier to inversion relative to an unsubstituted phenyl group (as is present in 33a ); T c = −49 °C for N -phenyl-2,2-dimethylaziridine .…”

Ab initio quantum chemical computations of substituent effects on triaziridine strain energy and heat of formation

“…Substituent effects on the pyramidal inversion barrier of aziridines and related nitrogen-containing small-ring heterocycles has been categorized as dominated by electronegativity, s p À , or s inv parameters. 79,82 Electronegativity effects can be related to ''Bent's rule'', 80 which states that, as the electronegativity of X becomes greater, the orbital, contributed to the bond by the partner atom to X, adopts more p character. In the case of an N-X bond, this means the lone pair must be more purely s in character and that should lead to an increase in the barrier.…”