Reactions of nitroalkenes with ynamines; synthesis of stable four-membered cyclic nitrones and X-ray crystal structure of 2-(NN-diethylcarbamoyl)-2,4-dimethyl-3-phenyl-2,3-dihydroazete 1-oxide

Abstract

S u m m a r y 2,3-Dihydroazete 1-oxides (3b-e), the first examples of crystalline, 'stable,' four-membered cyclic nitrones, are formed by reaction of 1-nitroalkenes with ynamines, and other products are 3-nitrocyclobutenes ;the structure of the cyclic nitrone (3b) has been determined by X-ray crystallography.CYCLOBUTENES are formed thermally under mild conditions either by reaction of electron-rich alkenes (e.g. enamines) with electron-deficient acetylenes [acetylene(di)carboxylic acid esters' 9 , or 1-t-butyl-2-nitr~acetylene~] or by reaction of electron-deficient alkenes (e.g. 1-cyanoalkenes) with electron-rich acetylenes (ynamines4 9 5 ) . We describe here the reactions of 1-nitroalkenes and ynamines.1-Nitrocyclopentene (la)6 was treated with an equimolar amount of l-phenyl-2-(pyrrolidin-l-yl)acetylene (2a) in light petroleum for 16 h at room temperature. A tan precipitate was filtered off,? and orange crystals (m.p. 80-81 "C; 40% yield) were obtained from the filtrate. This product was identified as the bicycloheptene (4a); lH n.ni.

Substituent and Solvent Effect Studies of N‐Alkenylnitrone 4π Electrocyclizations**

“…While studying factors that influence the rate of the 4π electrocyclization of N ‐alkenylnitrones, we also considered the potential reversibility of the reaction. Reports by Reinhoudt and co‐workers in the 1980s clearly show that amide and β‐styrenyl‐substituted azetidine nitrones, prepared via nitronate intermediates, can undergo cycloreversion to afford the corresponding N ‐alkenylnitrones (Scheme 3D) [14d,21] . Due to these reports, we were interested in evaluating the potential reversibility between 1 a and 2 a , and 1 b and 2 b , respectively.…”

“… [10] Solvent effects were noted to influence the time required for starting material conversion with unique dependencies for different substrates (Scheme 3C) [10] . In related investigations of azetidine nitrone cycloreversions reported by Reinhoudt and co‐workers for azetidine nitrones prepared from cyclic nitronate intermediates, the rate of N ‐alkenylnitrone formation was shown to be dependent on the extent of conjugation between the substituents and the azadiene (Scheme 3D) [14d,21] . These observations inspired us to undertake focused studies to better understand the substituent and solvent trends of the electrocyclizations of 1 to 2 and use this information to advance the development of the synthetic applications of azetidine nitrones.…”

Divergent Functionalizations of Azetidines and Unsaturated Azetidines

“…Reinhoudt reported the first synthesis of stable azetidine nitrones 132 via the addition of an electron‐rich ynamine to a nitroalkene followed by rearrangement (Scheme A) . While nitrocyclobutenes 131 and 2‐azadiene‐ N ‐oxides 133 were observed as competing byproducts when these transformations were run in petroleum ether, linear E ‐nitroalkenes were shown to favor the formation of azetidine nitrones 132 as single diastereomers and increased yields were observed in more polar solvents such as acetonitrile . The proposed mechanism for this transformation proceeds via a formal [4+2]‐cycloaddition between nitroalkene 127 and ynamine 128 to give 130 followed by N–O bond cleavage and azetidine cyclization.…”

Unexpected mode of reactivity in nitrosation of cis-1,1-dichloro-2,3-diphenylcyclopropane with NOCl·2SO3

“…Upon the whole the geometry of azetine cycle is closely related to that found for 2-(N,N-diethylcarbamoyl)-2,4-dimethyl-3-phenyl-2,3-dihydroazete-1-oxide. 4 The data of 1 H and 13 C NMR spectroscopy absolutely correspond to the results of X-ray crystallography. † Synthesis.…”