The Photochemical Mediated Ring Contraction of 4 H -1,2,6-Thiadiazines To Afford 1,2,5-Thiadiazol-3(2 H )-one 1-Oxides.
Emmanouil BroumidisChristopher G ThomsonBrendan GallagherLia SotorríosKenneth G McKendrickStuart A MacgregorMartin J PatersonJanet Eleanor LovettGareth O LloydGeorgina M RosairAndreas S KalogirouPanayiotis A KoutentisFilipe VilelaPublished in: Organic letters (2023)
1,2,6-Thiadiazines treated with visible light and 3 O 2 under ambient conditions are converted into difficult-to-access 1,2,5-thiadiazole 1-oxides (35 examples, yields of 39-100%). Experimental and theoretical studies reveal that 1,2,6-thiadiazines act as triplet photosensitizers that produce 1 O 2 and then undergo a chemoselective [3 + 2] cycloaddition to give an endoperoxide that ring contracts with selective carbon atom excision and complete atom economy. The reaction was optimized under both batch and continuous-flow conditions and is also efficient in green solvents.