ChemInform Abstract: Synthesis of a New Heterocyclic System - Pyrido[3′,2′:4,5]thieno[2,3-e][1,2,3]triazolo[1,5-a]pyrimidine

2002

benzopyran derivatives

benzopyran derivatives R 0350 Synthesis of New Heterocycles Through a Cation-Driven Tandem 48 - 142 Ring-Enlargement–Annulation Reaction. — Cyclobutachromenes (II) are formed by treatment of alcohols (I) in the presence of catalytic amounts of TosOH as result of intramolecular cyclization between a thionium ion, generated through cyclopropylcarbinyl/cyclobutyl ring expansion, and the activated aromatic ring. In the case of substrate (VIII), this reaction fails and only cyclobutanone (IX) is obtained. To demonstrate the synthetic versatility of compounds (II), controlled oxidations with MCPBA and desulfuration by Raney-Ni are performed. — (BERNARD, ANGELA M.; CADONI, ENZO; FRONGIA, ANGELO; PIRAS, PIER P.; SECCI, FRANCESCO; Org. Lett. 4 (2002) 15, 2565-2567; Dip. Sci. Chim., Complesso Univ. Monserrato, I-09042 Monserrato, Italy; EN)

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