Reaction of 3‐Amino‐2 H ‐azirines with 2‐Amino‐4,6‐dinitrophenol (Picramic Acid): Synthesis of Quinazoline‐ and 1,3‐Benzoxazole Derivatives

The reaction of 3‐(dimethylamino)‐2 H ‐azirines 1a–c and 2‐amino‐4,6‐dinitrophenol (picramic acid, 2 ) in MeCN at 0° to room temperature leads to a mixture of the corresponding 1,2,3,4‐tetrahydroquinazoline‐2‐one 5 , 3‐(dimethylamino)‐1,2‐dihydroquinazoline 6 , 2‐(1‐aminoalkyl)‐1,3‐benzoxazole 7 , and N ‐[2‐(dimethylamino)phenyl]‐α‐aminocarboxamide 8 ( Scheme 3 ). Under the same conditions, 3‐( N ‐methyl‐ N ‐phenyl‐amino)‐2 H ‐azirines 1d and 1e react with 2 to give exclusively the 1,3‐benzoxazole derivative 7 . The structure of the products has been established by X‐ray crystallography. Two different reaction mechanisms for the formation of 7 are discussed in Scheme 6. Treatment of 7 with phenyl isocyanate, 4‐nitrobenzoyl chloride, tosyl chloride, and HCl leads to a derivatization of the NH 2 ‐group of 7 ( Scheme 4 ). With NaOH or NaOMe as well as with morpholine, 7 is transformed into quinazoline derivatives 5 , 14 , and 15 , respectively, via ring expansion ( Scheme 5 ). In case of the reaction with morpholine, a second product 16 , corresponding to structure 8 , is isolated. With these results, the reaction of 1 and 2 is interpreted as the primary formation of 7 , which, under the reaction conditions, reacts with Me 2 NH to yield the secondary products 5 , 6 , and 8 ( Scheme 7 ).