Rotational barrier for 1-acetyl-2-(p-methoxy benzyl)-3-pyrroline

Calculation of the rotational barriers for the trans- and cis-forms of 2-(p-methoxy)-1-acetyl-pyrroline are presented in this paper. It is found that thetrans-isomer is slightly more favourable energetically, while the rotations of the cis-form are highly impeded. Hence the relevant rotations are in thetrans-form which stabilizes its energy by forming a weak inner proton bond between the carbonyl oxygen and the pyrroline ring. The acetyl rotational barrier is of the order of 8 kcal, which is well in accord with experimental data reported in the literature for other acetyl-amide derivatives.[/p]Work supported in part by Instituto Mexicano del Petróleo.     

Asymmetric Michael Addition of Aldimino Esters with Chalcones Catalyzed by Silver/Xing‐Phos: Mechanism‐Oriented Divergent Synthesis of Chiral Pyrrolines

The mechanism‐oriented reaction design for the divergent synthesis of chiral molecules from simple starting materials is highly desirable. In this work, aromatic amide‐derived nonbiarylatropisomer/silver (silver/Xing‐Phos) complex was used to catalyze the Michael addition of glycine aldimino esters to chalcones and successfully applied to the subsequent cyclocondensation to afford substituted cis‐Δ(1)‐pyrroline derivatives with up to 98 % ee. Besides the inherent performance of the chiral Ag/Xing‐Phos catalyst system, it was found that the workup of such reactions played an important role for the stereoselective construction of stereodivergent Δ(1)‐pyrrolines, in which an epimerization of the cis‐Δ(1)‐pyrrolines to the trans‐isomers during was revealed.     

Computational study of singlet and triplet sulfonylnitrenes insertion into 1,3‐butadienes: 1,2‐ or 1,4‐cycloaddition?

The formation of N‐trifluoromethylsulfonyl‐2‐vinylaziridine and N‐trifluoromethylsulfonyl‐3‐pyrroline by the reaction of the singlet and triplet trifluoromethanesulfonylnitrenes with s‐cis‐ and s‐trans‐1,3‐butadienes was studied theoretically at the B3LYP/6‐311++G(d,p) and M06‐2X/6‐311++G(d,p) levels of theory. The singlet trifluoromethanesulfonylnitrene adds to s‐cis‐ and s‐trans‐1,3‐butadiene exothermally in one step to give the product of 1,2‐cycloaddition, N‐trifluoromethylsulfonyl‐2‐vinylaziridine, the energy decreasing by 88.5 and 86.2 kcal/mol at the B3LYP level and by 105.2 and 103.0 kcal/mol at the M06‐2X level, respectively. The formed 2‐vinylaziridine can undergo rotation about the C(2)–C_sp2 bond with the barrier not exceeding 3.5 kcal/mol and to rearrange into N‐trifluoromethylsulfonyl‐3‐pyrroline. The triplet trifluoromethanesulfonylnitrene reacts with s‐cis‐ and s‐trans‐1,3‐butadiene in two steps. The first exothermic step is the formation of the triplet diradical adducts. The second step is the spin inversion with the energy raising by 5.8 and 17.8 kcal/mol at the B3LYP level and by 11.0 and 20.8 kcal/mol at the M06‐2X level for the adducts to s‐cis‐ and s‐trans‐1,3‐butadiene, respectively. Recombination of the radical centers occurs selectively to give N‐trifluoromethylsulfonyl‐2‐vinylaziridine that is exothermally rearranged into N‐trifluoromethylsulfonyl‐3‐pyrroline with the energy barrier of 40 kcal/mol at the B3LYP level and of 50 kcal/mol at the M06‐2X level. Copyright © 2014 John Wiley & Sons, Ltd.     

[1+1+3] Annulation of Diazoenals and Vinyl Azides: Direct Synthesis of Functionalized 1‐Pyrrolines through Olefination

A dirhodium carboxylate catalyzed [1+1+3] annulation reaction of diazoenals and vinyl azides that gives synthetically important enal‐functionalized 1‐pyrroline derivatives was developed. The reaction involves a novel rhodium‐catalyzed olefination of diazoenals with vinyl azides via electrophilic enal carbenoids, resulting in a new class of enal acrylates. The annulation reaction was used for the direct synthesis of valuable deuterated 1‐pyrrolines. Structural diversification of the enal‐functionalized 1‐pyrrolines resulted in the biologically important pyrrolidine‐fused oxaziridine, amino acid derivatives, and a 6‐azabicyclo[3.2.1]octane motif present in polycyclic alkaloids.     

Stereoselective electrocatalytic transformation of arylidenemalononitriles and malononitrile into (1R,5S,6R)-6-aryl-2-amino-4,4-dialkoxy-1,5-dicyano-3-azabicyclo[3.1.0]hex-2-enes

Electrolysis of arylidenemalononitriles and malononitrile in alcohols in an undivided cell in the presence of sodium bromide as mediator results in the stereoselective formation of (1R,2S,6R)^*-6-aryl-2-amino-4,4-dialkoxy-1,5-dicyano-3-azabicyclo[3.1.0]hex-2-enes in 60-80% yields.     

Stereoselective electrocatalytic transformations of malononitrile and aromatic aldehydes into (1<Emphasis Type="Italic">R</Emphasis>,5<Emphasis Type="Italic">S</Emphasis>,6<Emphasis Type="Italic">R</Emphasis>)*-4,4-dialkoxy-2-amino-6-aryl-1,5-dicyano-3-azabicyclo[3.1.0]hex-2-enes

Electrolysis of aromatic aldehydes and malononitrile in alcohols in an undivided cell in the presence of a NaBr-NaOAc mediatory system stereoselectively gave bicyclic compounds containing the cyclopropane and pyrroline fragments in 60 to 70% yields. In the bicyclic products, the benzene and pyrroline rings are on different sides of the cyclopropane ring.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 663–667, March, 2005.     

Synthesis of 2H-pyrroles by treatment of pyrrolidines with DDQ

A mild and efficient synthesis of 2,2-dialkyl-3,5-diaryl-2H-pyrroles is described. Treatment of 2,2-dialkyl-3,5-diarylpyrrolidines with DDQ in dioxane for 12-24 h at rt afforded the corresponding 2H-pyrroles in 55-81% overall yields.