| abstract |
Claim 1: A process for the preparation of a compound of the formula (1) or a salt thereof, which comprises the cycling of a compound of the formula (2) or a salt thereof, under reaction conditions sufficient to provide the compound of the formula (1) or one of its salts, where: R¹ is hydrogen or halo; R² is hydrogen or alkyl optionally substituted with aryl; R³ is hydrogen or a nitrogen protecting group; and R⁴ is hydrogen, or R³ and R⁴ together with the nitrogen to which they are attached form N-diphenylmethylene amine or a succinimide. |