Pyrrolin-2-ones, formation

Arylidene alkylamines and diphenyl cyclopropenone gave rise to products 397-399, whose formation can be interpreted by means of oxidative secondary reactions of the 5 H-A2-pyrrolin-4-one 396 (R2 = H) initially generated252. ... 

In a study of the flash vacuum pyrolysis of chiral isopropylidene N-isopropyl-N-(a-methylbenzyl)aminomethylenemalonates, (/ )- and (S)-(1239), McNab and Monahan demonstrated the existence of another intermediate (1242) in the reaction pathway from the methyleneketene (1240) to the pyrrolinone (1243) [87CC138 88JCS(P 1)869]. Pyrolysis of the enantiomers (R) and (S) of compound 1239 resulted in the formation of an enantiomeric mixture of l-isopropyl-5-methyl-5-phenyl-2-pyrrolin-5-one (1243), where incomplete chirality loss was observed (see Scheme 50). 

In this type of spin traps, 5,5-dimethyl-l-pyrroline-Af-oxide (DMPO) deserves particular mention. DMPO is widely employed as a spin trap in the detection of transient radicals or ion-radicals in chemical and biological systems (see, e.g., Siraki et al. 2007). Characteristic ESR spectra arising from the formation of spin adducts are used for identification of specific spin species. In common opinion, such identification is unambiguous. However, in reactions with superoxide ion (Villamena et al. 2004, 2007b), carbon dioxide anion-radical (Villamena et al. 2006), or carbonate anion-radical (Villamena et al. 2007a), this spin trap gives rise to two adducts. Let us consider the case of carbonate anion-radical. The first trapped product arises from direct addition of carbonate anion-radical, second adduct arises from partial decarboxylation of the first one. Scheme 4.25 illustrates such reactions based on the example of carbonate anion-radical. 

Perhydropyrrolo[l,2-fc]isoxazoles result from 1,3-dipolar cycloaddition of cyclic nitrones with alkenes. The high regio- and stereoselectivity of this cycloaddition has been used to control the stereochemistry in the synthesis of natural products. As one example, pyrroline N-oxide (70) and 3,4-dimethoxystyrene gave a diastereomeric mixture of pyrroloisoxazoles (71) and (72), in nearly quantitative yield with preferential formation of (71). 

The polymeric pyrrolic autoxidation products probably result from the oxidized monomeric systems, which are analogous in structure to those isolated from photooxidation and peroxide oxidation reactions. Thus, for example, analysis of the products of the autoxidation of 1-methylpyrrole (Scheme 47) would suggest that 1 -methyl-A3-pyrrolin-2-one (153) is initially formed from a radical reaction of the pyrrole with triplet oxygen. This reaction sequence should be compared with that proposed for the oxidation of pyrroles with hydrogen peroxide (Scheme 50), which yields (181), (182) and (183) as the major isolable products. The acid-catalyzed reaction of a pyrrole with its oxidation product e.g. 153) also results in the formation of polymeric material and the formation of pyrrole black is probably a combination of oxidation and acid-catalyzed polymerization processes. 

One route of catabolism of proline is essentially the reverse of its formation from glutamate. Proline oxidase yields A -pyrroline 5-carboxylate.145a,b... 

This results in a predicted enthalpy of formation of 3H-indole of 193 kJmol-1. That this value is so close to that suggested in the literature gives credence to the enthalpies of formation of both 3H-indole and the earlier one cited above for A pyrroline. We are encouraged163. 

The absolute configuration of (-l-)-physoperuvine, and of its N-benzoyl derivative, was determined by the positive Cotton effect around 290 nm, in the region exactly as reported5 for (R)-(+)-3-methylcycloheptanone. The racemic form accompanies the optically active one in the plant they were separated by column chromatography. Since tropane alkaloids form in vivo from ornithine via A-pyrroline,6 the biogenetic role of secotropanes is likely to be that of products of degradation rather than of intermediates in the formation of the tropane bases. 

Irradiation of a ferf-butyl alcohol solution of 2-ethoxy-pyrroline-5-one (12) with Vycor filtered light from a 450-W mercury lamp results in formation of ferf-butyl N-(ethoxycyclopropyl) carbamate (13) in 73% isolated yield17,18 When the irradiation is conducted in the non-hydroxylic solvent, tetrahydrofuran, 1-ethoxycyclo-propyl isocyanate (20) can be isolated in 78% yield. Both 13 and 20 can be prepared in synthetically useful quantities. 

The reaction of 5,5-dimethyl-l-pyrroline 1-oxide with dimethylketene N-phenylimine leading to pyrrolo[l,2-a]imidazol-2(3H)-ones (190) proceeds via initial formation of zwitterion (188). Subsequent sigmatropic rearrangement of (188) gives zwitterion (189), capable of undergoing ring closure to (190) (79JOC4543). 

Annelation of steroidal dienamines with substituted phenacyl bromides (7 examples) or with benzenediazonium salts (11 examples) has been shown to lead to the corresponding furano- and indolo-steroids.89 Thus the A3,5-dienamine derived from A4-androstene-3,17-dione reacted with p-bromophenacyl bromide to yield the A5-androstano[3,4-h]furan (199) in 26% yield, and reaction of the same A3,5-dienamine with benzenediazonium fluoroborate at -45 °C led to formation of the hydrazone (200) which underwent Fischer-indole cyclization on treatment with phosphorus oxychloride to produce the A4-androstano[6,7-6]indole (201). The A3,5-dienamine derived from 17/3-acetoxyandrost-4-en-3-one has been converted into the benz[4,5,6]-steroid (202 R1 = Me, R2 = H) by reaction with methyl vinyl ketone and into the analogous benzsteroid (202 R1 = H, R2 = Me) on treatment with crotonal-dehyde.90 A route to the condensed pyrroline ring system (203) has been devised... 

Taking advantage of an intramolecular Wittig reaction, the a-amidoketones 316 underwent annulation to the 3-pyrrolines 317 upon treatment with the ylide 318 <199581151>. These intermediates could be further elaborated to the pyrroles 319 by base-induced elimination of benzenesulfinic acid (Scheme 37) <2000TL8969>. It should also be mentioned that a set of unusual 3-pyrroline-2-ones have been synthesized by Ugi s four-component reactions from phenacylamine hydrochloride, cyanoacetic acid, cyclohexyl isocyanide, and aldehydes, involving final formation of the C(3)-C(4) bond <1999H(50)463>. 

Photochemical rearrangements have also been reported, as shown in equation (53). " Transition metal catalyzed rearrangement [palladium(O)] of a dienylaziridine has been reported in one case, and a radical opening of a dienylaziridine led to pyrroline formation under the conditions of radical initiation with AIBN/PhsSnH (equation 54). For those vinylaziridines that contain additional unsaturation, the corresponding aza equivalent of a divinylcyclopropane Cope rearrangement is the usual pathwayThe subject of heterodivinylcyclopropane Cope rearrangement is covered in detail elsewhere." The... 

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