Synthesis of pyrazolo[3,4-b]pyrrolo[3,4-d]pyridine derivatives via Aza-Diels–Alder reaction: evaluation of torsion effect of pyrazoylimines

A modified method for the synthesis of pyrazolo[3,4-b]pyrrolo[3,4-d]pyridine was developed through an Aza-Diels–Alder reaction of pyrazoylimines with maleimides in the sealed tube. Based on the control experiment, the yields for the Aza-Diels–Alder reaction seemed proportional to the suitable torsion conformation of pyrazoylimine, which was modulated by N,N-disubstituted amidinyl moiety. The versatile sealed tube technique was also proved to promote the higher isolated yields in the Aza-Diels–Alder reaction.

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