N‐Aroylsulfonamide‐Photofragmentation (ASAP)‐A Versatile Route to Biaryls

Abstract

In memory of Klaus HafnerThe photochemical fragmentation of N-aroylsulfonamides 9 (ASAP) is a powerful method for the preparation of various biaryls. Compounds 9 are easily accessible in two steps from amines by treatment with arenesulfonyl chlorides and aroyl chlorides. Many of these compounds were prepared for the first time. The irradiation takes place in a previously developed continuous-flow reactor using inexpensive UVB or UVC fluores-cent lamps. Isocyanates and sulphur dioxide are formed as the only by-products. The ASAP tolerates a variety of functional groups and is even suited for the preparation of phenylnaphthalenes and terphenyls. The ASAP mechanism was elucidated by interaction of photophysical and quantum chemical (DFT) methods and revealed a spirocyclic biradical as key intermediate.

Light-Driven Reductive Cleavage of Sulfonamides Promoted by Thiourea Organophotosensitizers

“…13 C­{ 1 H} NMR (125 MHz, CDCl 3 ): δ 143.6, 135.8, 129.8, 127.3, 29.4, 21.6 ppm. Spectroscopic data were consistent with the literature data for this compound …”

“…According to the representative procedure, starting from methylamine (33 wt % in absolute ethanol, 1 equiv, 300 mg, 3.19 mmol) and tosyl chloride (1.1 equiv, 668 mg, 3.51 mmol); compound S8 (300 mg, 1.62 mmol, 51%) was isolated as a white solid. 1 42 Compound S9. According to the representative procedure, starting from N-methylethylenediamine (1 equiv, 0.12 mL, 1.35 mmol) and tosyl chloride (2 equiv, 728 mg, 2.70 mmol); flash chromatography on silica gel (EtOAc/Cy, 1:1) gave compound S9 (226 mg, 0.59 mmol, 44%) as a white solid.…”

Sustainable and highly controlled aryl couplings revealed by systematic assessment of photoactivatable linkers

“…Recently, a similar method using N -methyl-aroylsulfonamides has been reported, but this procedure is less attractive from an environmental point of view because toxic methyl isocyanate is formed as the byproduct. 17…”

“…Recently, a similar method using N-methyl-aroylsulfonamides has been reported, but this procedure is less attractive from an environmental point of view because toxic methyl isocyanate is formed as the byproduct. 17 We have also replaced the carbonyl in 1k for a sulfone group to give bis-sulfonimide 1l, which has a linker containing two sulfone groups. In analogy to sulfonamides, this functional group also undergoes rearrangement upon exposure to UV light to form biphenyl 2a, yet only in trace amounts.…”

Light-driven reductive cleavage of sulfonamides promoted by thiourea organophotosensitizers

“…Spectroscopic data were consistent with the literature data for this compound. 42 Compound S9. According to the representative procedure, starting from N-methylethylenediamine (1 eq., 0.12 mL, 1.35 mmol) and tosyl chloride (2 eq., 728 mg, 2.70 mmol); flash chromatography on silica gel (EtOAc/Cy, 1:1) gave compound S9 (226 mg, 0.59 mmol, 44 %) as a white solid.…”