[2 + 2] Cycloadditions of lithium alkynamides produced by fragmentation of 5-lithio-1-phenyl-1,2,3-triazoles

Abstract

Three 1-phenyl-1,2,3-triazoles 1a–c bearing substituents at the 4-position have been converted into the corresponding 5-lithio compounds. These undergo fragmentation and loss of nitrogen at room temperature. The N-phenylalkynamide salts 3 so produced have been intercepted in [2 + 2] cycloadditions. The salt derived from the triazole-4-carboxamide 1b reacts with cyclohexanone and with 4-chlorobenzaldehyde by cycloaddition to the CO bond; the cycloadducts then undergo ring-opening and the amides 5 and 7 are isolated. Analogous reactions are observed with the 4-(dihydroloxazol-2-yl)triazole 1c: in this case the lithium salt also reacts with a Schiff base, 4-chloro-α-phenyliminotoluene, and with an electrophilic alkene, dimethyl fumarate. A cyclobutene diester, compound 12, has been isolated from this last reaction. The lithium salt 3a derived from 1,4-diphenyltriazole 1a has similarly been intercepted by dimethyl fumarate and by nitrostyrenes. Structures 13 and 14 have been assigned to the products of these reactions.