Visible-light-mediated sequential Wolff rearrangement and Staudinger cycloaddition enabling the assembly of spiro-pyrazolone-β-lactams

Abstract

Visible-light-mediated sequential Wolff rearrangement and Staudinger cycloaddition for the assembly of valuable spiro-pyrazolone-β-lactams for the first time is disclosed by utilizing in situ generated ketenes and pyrazolone ketimines. This powerful...

Cooperative photoactivation/Lewis base catalyzed [4 + 2] annulations of α-diazoketones andortho-amino MBH carbonates to access dihydroquinolinone frameworks

“…Based on the obtained results and previous literature, 14 a , b ,21 a plausible reaction mechanism was proposed in Scheme 3B. The first SN2′ process was triggered by the nucleophilic attack of Lewis base catalyst (NR 3 ), the leaving group –OBoc was decomposed to CO 2 and t BuO − , and then t BuO − grabbed the hydrogen from amide delivering t BuOH and Int-1 .…”

Lighting the way to diverse cyclic architectures: expanding the horizons with photogenerated ketenes in sustainable chemistry

“…In 2022, our group established a visible-light-mediated sequential reaction strategy that combines Wolff rearrangement with Staudinger cyclization, using in situ generated ketenes I and pyrazolone ketimines 2 to create valuable spiro-pyrazolone-β-lactams 3 (Scheme 2). 33 This approach offers a reliable solution for synthesizing spiro-pyrazolone-β-lactams with high yields, excellent substrate tolerance, and gram-scale production while providing direct access to multisubstituted pyrazole-morpholine skeletons. Optimization of the reaction conditions revealed that the wavelength of visible-light plays a critical role in enhancing reaction rates, and controlled experiments demonstrated the importance of visible-light-mediated irradiation in cyclization.…”

Synthesis of tetracyclic dibenzo[b,f][1,4]oxazepine-fused β-lactams via visible-light-induced Staudinger annulation

“…10 Recently, our research group reported a visible-light-induced catalyst-free Wolff rearrangement/domino [4 + 2] cycloaddition of 2-benzothiazolimines with α-diazo ketones for the efficient synthesis of benzothiazolopyrimidine bearing a quaternary carbon center. 11 According to recent reports, 12 we envisioned that the synthesis of tetracyclic dibenzo[ b , f ][1,4]oxazepine-fused β-lactams bearing a quaternary carbon center could be realized by visible-light-induced Staudinger [2 + 2] annulations of α-diazo ketones. Herein, we report a visible-light-induced Staudinger [2 + 2] annulation reaction between α-diazo ketones and dibenzo[ b , f ][1,4]oxazepine/thiazepine-imines under catalyst-free conditions.…”