Nitrile ylides substituent effects

Some interesting work has been carried out on the generation and reactions of nitrile ylides (e.g., 164 and 171) with different substituents at the nitrile carbon. The effect of such substituents on regioselectivity in cycloaddition reactions throws... 

Substituent Directive Effects in the Cyclization of Nitrile Ylides 18... 

Inductive effects exerted by substituents on the nitrile ylide also have an important effect on the regio-selectivity of the cycloaddition. Benzonitriliohexafluoro-2-propanide (73) and methyl acrylate yield products with inverse regioselectivity, as compared with the reactions of the related benzonitrilio-2-pro-panide (76 Scheme 18).83 The difference in regioselectivity has been attributed to the larger coefficient... 

Supercritical carbon dioxide with a minute co-solvent addition is an effective medium for the 1,3-dipolar cycloaddition of azomethine ylides with DMAD to produce substituted pyrroles.67 The 1,3-dipolar cycloaddition of nitrile ylides [e.g. benzonitrile (4-nitrobenzylide) and 4-nitrobenzonitrile(benzylide)] with acrylamides provided a synthesis of 3,4-dihydro-2//-pyrroles with moderate to good yields.68 The Pt(II)-or Au(III)-catalysed 3 + 2-cycloaddition of the transition metal-containing azomethine ylide (63) with electron-rich alkenes provided a carbene complex (64), which yields tricyclic indoles (65) having a substituent at 3-position (Scheme 17).69 The 1,3-dipolar cycloadditions of azomethine ylides with aryl vinyl sulfones are catalysed by Cu(MeCN)4C104-Taniaphos with nearly complete exo- selectivity and enantioselec-tivities up to 85% ee.10 The 3 + 2-cycloaddition of benzol/>]thiophene 1,1-dioxide... 

The full synthetic potential of nitrile ylides in 1,2,4-triazoline synthesis has not yet been explored the few available studies are confined to reactions with symmetrical dipolarophiles. Substituent effects of unsymmetri-cal dipolarophiles on the regiochemistry of triazoline formation are not known. 

Groundwater, P.W., and Sharp, J.T., Electrocyclic aromatic substitution by nitrile ylides to give 37/-2-benzazepines. Substituent effects and mechanism. Tetrahedron. 48. 7951, 1992. 

The results show that when the energy difference between the nonplanar bent and linear forms is small, substituent effects can play an extremely important role in determining the course of the intramolecular cycloaddition reactions of nitrile ylides. The formation of a mixture of 1,1 and 1,3 cycloadducts from the irradiation of 219 has been attributed to the fact that the energy levels of the bent and linear forms must lie very close to each other. The isolation of both 1,1 and 1,3 cycloadducts from the irradiation of 222 is related to the fact that the methyl substituent on the double bond diminishes the rate of 1,3-dipolar cycloaddition and enhances the rate of the 1,1 cycloaddition. 

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