One-pot domino synthesis of five- and six-membered fused dihydropyridines promoted by PPh₃–NBS in aqueous medium

Abstract

A facile one pot synthesis of five and six-membered fused dihydropyridines such as chromenodihydropyridines, pyrazolodihydropyridines and isoxazolopyridines are accomplished by employing PPh3-NBS via a formal [3+2+1] cycloaddition of 1,3-bisnucleophiles (i.e.,...

Modular and selective synthesis of pyrazolo-azepino-centred polycyclic aromatic and non-aromatic architectures

“…In addition, the C4 position of 5-aminopyrazole is also nucleophilic, so it could attack the aldehyde irreversibly, dividing the domino stream (Scheme 2c). 15 Second, the use of a united domino approach to selectively prepare aromatic and non-aromatic polycycles is scarce and in principle risky since the oxidation step usually occurs sequentially after the skeleton construction, and thus the oxidant may interfere with the ring formation process during the one-pot reaction. 16 Our solution to this problem was to use an endogenous oxidant that also plays a necessary role in the skeleton construction stage to further realize downstream aromatization.…”

Switchable Chemoselectivity in [3 + 3] Annulation of β,γ-Unsaturated α-Ketoesters and 1H-Pyrazol-5-amines by Cooperative Acid Catalysis with NiII and InI

“…1 H- Pyrazolo[3,4- b ]pyridine and dihydro-1 H -pyrazolo[3,4- b ]pyridine derivatives are privileged structural motifs, occurring frequently in numerous natural products, pharmaceuticals, and biologically active molecules (Figure ). − Therefore, numerous efforts have been devoted to developing efficient catalysts for the selective addition of α,β-unsaturated carbonyls with 1 H- pyrazol-5-amines. − Although many efforts have focused on the α,β-unsaturated carbonyls in formal [3 + 3] cycloaddition with enamines, − the exploitation of β,γ-unsaturated α-ketoesters remains less studied. − This is speculatively attributed to chemoselectivity issues arising from the differentiation of 1,2- and 1,4-addition pathways. In 2010, we first developed asymmetric binary-acid catalysis, which resulted in a synergistic effect for catalysis in regio-, diastereo-, and enantiodivergent , reactions.…”