A novel route to unsymmetrical stilbene derivatives via intramolecular free radical ipso substitution reactions

Synthesis of heterocycles by radical cyclisation

“…103 Motherwell and co-workers have carried out several syntheses of unusual S-heterocycles involving cyclisation of aryl radicals onto side chains containing sulfonates and sulfonamides. [104][105][106] In Scheme 29 the synthesis of a biphenyl system containing a seven membered ring sulfonamide is shown as an illustration of this methodology. 104 The benzylic N-methylsulfonamide 109 is converted to the cyclised sulfonamides 110 and 111.…”

“…4-Aryl-5,6-dihydro-1,2-oxathiine 2,2-dioxides and related heterocyclic systems have been synthesised using this protocol which also involves an unusual rearrangement reaction via radical addition to aryl and heteroaryl rings. 106 The other characteristic of radical reactions involving sulfur atoms which is uncommon for those involving nitrogen or oxygen atoms is the ability to undergo β-scission to give intermediate thiyl radicals. A number of examples in the literature have shown the synthetic potential of using this behaviour for the preparation of thiophenes, 107 dihydrothiophenes 108 and 2,3dihydrobenzothiophenes.…”

Titanocene-Mediated Intramolecular Radical Vinylations

“…Examples of the former involve sulfides 10 and sulfonamides. 11 In the course of previous work, we serendipitously observed that silicon groups could be radical leaving groups under special circumstances. 12 This led us to think about the potentialities offered by the radical b-elimination tool, which we felt could open the way to enantioselective vinylations (Caddick had showed that a similar strategy using racemic sulfoxides could lead to the formation of polycyclic heterocycles 13 ).…”

Copper(I) Halide Mediated Tandem 1,4-Aryl Migration-Oxidative Amidyl Radical Cyclisation of Bromosulfonamides

“…Although we postulated that oxindole 8b was likely formed via cyclisation of 11 (11 → 12 → 13 → 8b) we could not rule out its formation from extrusion of SO 2 from the undetected cyclic sulfonamide 15 (i.e., 15 → 16b where 16b = 8b). 13 In order to probe this further we prepared the 4-tolyl derivative 1c 2 and investigated its reaction with CuBr-7 under two sets of conditions (CH 2 Cl 2 , 40°C, 18 h and toluene, 110°C, 24 h). By analogy to 1b the expected products would be the 2-aryl amide 3c and the 6-methyl oxindole 8c (assuming pathway 11 → 12 → 13 → 8c) or 5-methyl oxindole 16c (assuming pathway 9 → 14 → 15 → 16c).…”

“…By analogy to 1b the expected products would be the 2aryl amide 3c and the 6-methyl oxindole 8c (assuming pathway 11 → 12 → 13 → 8c) or 5-methyl oxindole 16c (assuming pathway 9 → 14 → 15 → 16c). We also prepared authentic samples of both of these oxindoles 8c and 16c via an intramolecular Friedel-Crafts acylation of the corresponding amides 17 and 18 (Scheme 3) and key 1 H NMR and 13 C NMR data are presented. 14 As observed for compound 1b the nature of the solvent and the temperature at which the reaction was carried out affected the ratio of products.…”