Action of tert-butyl azidoformate on the conjugate bases of 1,2,3,4-tetrahydro-9H-carbazole and other indole derivatives

tert-Butyl azidoformate (2) reacts with the conjugate bases of 3a, 7a, 9 (R1 = R2 = CH3), and 9 (R1 = CH3, R2 = H) to give products [4, 8, 12, and 14, respectively] in addition to the expected N-(tert-butoxycarbonyl)indole derivatives.