The Effects of Lewis Acid on the 1,3-Dipolar Cycloaddition Reaction of C-Arylaldonitrones with Alkenes.

Abstract

Absence of Lewis AcidThe reaction of N-benzyl-C-phenylnitrone (1a) with a variety of mono-and 1,1-disubstituted alkenes (2A-P) was carried out under various conditions and the results ware * To whom correspondence should be addressed. The regio-and stereoselectivity of the 1,3-dipolar cycloaddition reactions of C-aryl-N-alkylaldonitrones (1a-e) with some alkenes were found to be affected significantly by the addition of Lewis acid. The rate of the reaction was also affected by adding the Lewis acid. In the reactions using allyl alcohol as a dipolarophile an addition of Lewis acid caused a remarkable acceleration of the reaction and a great change in the stereoselectivity. In the reactions using ethyl acrylate as a dipolarophile the regioselectivity was reversed whether the reaction was performed in the presence or the absence of Lewis acid; i.e. isoxazolidine-5-carboxylates were obtained mainly in the absence of Lewis acid although isoxazolidine-4-carboxylates were obtained mainly in the presence of Lewis acid. When the reaction of C,N-diarylaldonitrones (1k, 1m, 1n) with ethyl acrylate was carried out in the presence of Lewis acid, the cleavage of the N-O bond of the cycloadducts giving g g-aminoalcohols was also observed besides a reverse phenomenon of regioselectivity.

Stereochemistry of cycloaddition of (S)-N-(1-phenylethyl)-C-diethoxyphosphorylated nitrone with vinyl acetate. Studies on mutarotation of 3-(O,O-diethylphosphoryl)-5-hydroxyisoxazolidines

“…1). Several achiral as well as chiral nitrones have been examined in the reaction with vinyl acetate including synthetic, [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21] as well as theoretical studies. 15,22 Since 5-acetoxyisoxazolidines could be used as starting materials in the Vorbrü ggen reaction, 23 the synthesis of isoxazolidine analogues of nucleosides became apparent.…”

“…Hz, 3H, CH-CH 3 ), 1.25 (t, J = 6.7 Hz, 3H, CH 3 -CH 2 -OP) 13. C NMR (CDCl 3 ): d 141.17, 128.68, 128.28, 127.88, 64.93 (d, J = 16.6 Hz, CH-Ph), 64.90 (d, J = 9.0 Hz, C5), 62.94 (d, J = 6.3 Hz, CH 2 OP), 57.23 (d, J = 149.2 Hz, C3), 25.39 (very br s, C4), 20.70 (s, CH 3 -CH), 16.67 (d, J = 5.4 Hz, CH 3 CH 2 OP).…”

A Convenient New Synthesis of 3‐Substituted β‐Lactams Formally Derived from 1‐(Aminomethyl)cyclopropanecarboxylic Acids

“…As could be expected from literature precedents,7 1,3‐dipolar cycloadditions of N ‐benzyl‐ C ‐(methoxycarbonyl)nitrone ( 3a ),8 N ‐benzyl‐ C ‐phenylnitrone ( 3b ),9 N ‐benzyl‐ C ‐cyanonitrone ( 3c ),10 N ‐( p ‐methoxybenzyl)‐ C ‐cyanonitrone ( 3d ), N ‐methyl‐ C ‐phenyl‐ ( 3e ) and N ‐methyl‐ C ‐(2pyridyl)nitrones ( 3f )11 to bicyclopropylidene ( 2 ) in benzene at ambient or elevated temperature gave the corresponding cycloadducts 5a − f in 100, 95, 94, 100, 93 and 71% yields, respectively (Scheme ). As in previous cases, for those cycloadditions that were carried out at moderate temperatures in order to avoid the thermal rearrangement of the cycloadducts 5 at elevated temperature, very long reaction times were necessary (cf.…”

Diethyl Cyclopropylidenemalonate: Facile Preparation, Generation in situ, and Various Transformations

“…[1,22] The potential to trap 3-Et generated in situ directly with various reagents in high yields and to use a storable, stable precursor such as the acetate 11 promises possible future applications of 3-Et in combinatorial chemistry to build small molecule libraries. [10] 4-methoxyphenyl-N-phenylnitrone (13a), [23] and 2-pyridyl-N-methylnitrone (13b) [24] were prepared by previously published procedures. All operations in anhydrous solvents were performed under argon in flame-dried glassware.…”