Synthesis of Trans/Cis ‐Benzo[f,h]Isoquinolin‐1(2 H )‐Ones via Photo 6π‐Electrocyclization

ABSTRACT We developed a photoinduced 6π‐electrocyclization method to synthesize a series of trans/cis‐ benzo[f,h]isoquinolin‐1(2 H )‐ones . Trans ‐2‐methyl/2,4a‐dime thyl‐4a,12b‐dihydrodibenzo[f,h]isoquinolin‐1(2 H )‐ones ( trans ‐2a–2h , trans ‐2i–2l) and trans ‐3,10b‐dimethyl/3‐methyl/10b‐methyl‐4a,10b‐dihydrobenzo[f]isoquinolin‐4(3 H )‐ones ( trans ‐4a–4i , trans ‐4j) were obtained by irradiating 3‐([1,1′‐biphenyl]‐2‐yl)‐1‐methyl/1,4‐dimethylpyridin‐2(1 H )‐ones ( 1a–1h and 1i–1l) and ( E )‐1,4‐dimethyl/1‐methyl/4‐methyl‐3‐styrylpyridin‐2(1 H )‐ones ( 3a–3j) under UV light, respectively. In the presence of HCl, cis ‐ 2a–2h and cis ‐4a–4i were synthesized under the same conditions of trans ‐ 2a–2h and trans ‐4a–4i . Cis ‐2i–2l and cis ‐4j were prepared by heating trans ‐2i–2l and trans ‐ 4j in DMF at 110°C. The transformation proceeds via a photo 6π‐electrocyclization followed by a [1,5‐ H ] shift, enabling the efficient construction of dearomatized trans/cis‐ benzoquinolin‐2(1 H )‐one scaffolds with high atom economy and effective bond formation. This method provides a metal and additive‐free strategy for the concise synthesis of chemoselectively trans/cis‐ benzoquinolinone frameworks.