A complicated path of salicylaldehyde through the Biginelli reaction: a case of unexpected spiroketalization

Cyclocondensation of salicylaldehydes with alkyl acetoacetates and 2-aminobenzothiazoles or 2-amino-5-methylthiazole under classical Biginelli reaction conditions gives rare hetarylamino substituted 2,2′-spirobischromanecarboxylate derivatives. The mechanism and observed stereoselectivity of the unexpected pseudo-four-component process are discussed.

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