1,3-dipolar cycloaddition reactions of organic azides with morpholinobuta-1,3-dienes and with an α-ethynyl-enamine

The cycloaddition of organic azides with some conjugated enamines of the 2-amino-1,3-diene, 1-amino-1,3-diene, and 2-aminobut-1-en-3-yne type is investigated. The 2-morpholinobuta-1,3-diene 1 undergoes regioselective [3 + 2] cycloaddition with several electrophilic azides RN3 2 (a, R = 4-nitrophenyl; b, R = ethoxycarbonyl; c, R = tosyl; d, R = phenyl) to form 5-alkenyl-4,5-dihydro-5-morpholino-1H-1,2,3-triazoles 3 which are transformed into 1,5-disubstituted 1H-triazoles 4a,d or alpha,beta-unsaturated carboximidamide 5 (Scheme 1). The cycloaddition reaction of 4-[(1E,3Z)-3-morpholino-4-phenylbuta-1,3-dienyl]morpholine (7) with azide 2a occurs at the less-substituted enamine function and yields the 4-(1-morpholino-2-phenylethenyl)-1H-1,2,3-triazole 8 (Scheme 2). The 1,3-dipolar cycloaddition reaction of azides 2a-d with 4-(1-methylene-3-phenylprop-2-ynyl)morpholine (9) is accelerated at high pressure (ca. 7-10 kbar) and gives 1,5-disubstituted dihydro-1H-triazoles 100 and 1-phenyl-5-(phenylethynyl)-1H-1,2,3-triazole (11d) in significantly improved yields (Schemes 3 and 4). The formation of 11d is also facilitated in the presence of an equimolar quantity of tBuOH. The three-component reaction between enamine 9, phenyl azide, and phenol affords the 5-(2-phenoxy2-phenylethenyl)-1H-1,2,3-triazole 14d.