Chemistry of dihydropyridines. 9. Hydride transfer from 1,4-dihydropyridines to sp3-hybridized carbon in sulfonium salts and activated halides. Studies with NAD(P)H models

Abstract

ether gave pure la (30 mg, 15%): mp 188-189 "C; NMR7 (acetone-d6 + DzO) d 3.04 (s, 3, CH3), 4.38 (d of q, 1, H3), 4.78 (d, 1, H4), 6.08 (d of d, 1, Hz), 7.25-8.25 (m, 7, H1 and aromatic), 8.73 trans-3,4-Dihydroxy-anti-1,2-epoxy-1,2,3,4-tetrahydro-7methylbenz[a]anthracene (2). A solution of la (23 mg, 0.083 mmol) and rn-chloroperbenzoic acid (230 mg) in 25 mL of dry THF was stirred under Nz for 2 h at room temperature. The solution was diluted with ether, washed twice with 10% aqueous NaOH solution and water, and dried. Evaporation of the solvent (avoiding heating), followed by trituration with ether, gave 2 (13 mg, 57%) as a white solid: mp 183-185 "C; NMR ( a~e t 0 n e -d~ 4.88 (d, 1, H4), 5.40 (d, 1, H1), 7.38-8.41 (m, 6, aromatic), 8.85 (s, trans -1,2-Dihydroxy-an ti -3,4-epoxy-1,2,3,4-tetrahydro-7methylbenz[a]anthraoene (4a). Epoxidation of 3a (23 mg, 0.08 mmol) was carried out by the procedure employed for the analogous reactions of la. Evaporation of the solvent (avoiding heating) gave crude 4a (20 mg, 74%) which showed one major peak (80%) on LC on a Ihpont Si1 column (THF-heptane, 4555). The major peak was collected and identified as 3a: NMR (acetone-d6 + The reactions of 1,2,6-trimethyl-3,5-bis(methoxycarbonyl)-l,4-dihydropyridine (2a), l-methyl-3,5-bis(methoxycarbonyl 1-1,4-dihydropyridine (2b), and l-benzyl-3-acetamido-1,4-dihydropyridine (1) with various sulfonium salts have been investigated. On thermal (60 "C) activation 2a,b react with, for example, methylphenacylphenylsulfonium tetrafluoroborate (3b) to give the respective pyridinium salts, acetophenone, and phenyl methyl sulfide. There is some competing isomerization of the 1,4-dihydropyridines to their (nonreactive) 1,2-dihydro isomers, this being catalyzed by the pyridinium salt formed on reduction of the sulfonium salt. Phenacyl-, acetonyl-, and in some cases benzylsulfonium salts can be reduced. The group to which hydride transfer takes place should be electron deficient. These reductions can be initiated at rwm temperature with visible light (at rmm temperature pyridinium :salt induced isomerization of the 1,4-dihydropyridine to its 1,2 isomer occurs only over a period of several days:i. The effect of visible light can be enhanced greatly by adding small amounts of dyes to the reaction mixtures. Eosin sodium salt, tetraphenylporphine, and R~"(2,2'-bpy)~Cl~ are all capable of increasing the rate of reduction; the last dye is by far the most effective. The results of mechanistic investigations are consistent with the hypothesis that the light-induced reductions are one-electron transfer reactions. In some cases there appears to be a separate thermal mechanism not sensitive to either light or sensitizers. Some sulfonium salts react with dihydropyridines to give the pyridinium salt and sulfide in less than quantitative yield and no reduction products from the sulfonium salt. As determined for the case of the reaction of bromomalonitrile with 1, and presumably also for other reactions, alkylation of an enamine carbon in the dihydropyridine is ...

Photoredox catalysis by [Ru(bpy)3]2+ to trigger transformations of organic molecules. Organic synthesis using visible-light photocatalysis and its 20th century roots

“…2 m distance). Addition of SCHEME 2 Dye-accelerated photoreduction of phenacyl sulfonium salt 2 and related substrates (refs 16,17 ) 1 mole % of [Ru(bpy) 3 ]Cl 2 , TPP, or eosin disodium salt led to acceleration of the irradiated reactions resulting in complete conversions within significantly shorter reaction times of 0.3, 1 and 3 h, for the three dyes, respectively. The authors suggested that light-induced single-electron transfer steps are responsible for the observed sulfonium salt reduction and proposed that the large acceleration effect of [Ru(bpy) 3 ]Cl 2 might be due to the involvement of this photoredox catalyst in the single-electron transfers (SET) 16 .…”

“…The authors suggested that light-induced single-electron transfer steps are responsible for the observed sulfonium salt reduction and proposed that the large acceleration effect of [Ru(bpy) 3 ]Cl 2 might be due to the involvement of this photoredox catalyst in the single-electron transfers (SET) 16 . Later on, results of a more detailed mechanistic study were disclosed 17 . Although the authors did not arrive at a definitive conclusion about the exact role of [Ru(bpy) 3 ] 2+ in this process, an impressively insightful discussion of the gathered body of evidence was presented 17 .…”

“…Later on, results of a more detailed mechanistic study were disclosed 17 . Although the authors did not arrive at a definitive conclusion about the exact role of [Ru(bpy) 3 ] 2+ in this process, an impressively insightful discussion of the gathered body of evidence was presented 17 .…”

“…Reductions of other substrates such as ammonium, phosphonium salts, and 4-nitrobenzyl halides have been also achieved (5, 6, 7a and 7b, respectively, Scheme 2) 16,17 . In 1985, the same group described reductions of phenacylbromide, bromomalonates, and related substrates (Scheme 3) using 3-methyl-2,3-dihydrobenzothiazoles using [Ru(bpy) 3 ]Cl 2 or rose bengal as photocatalysts 18 .…”

Block Copolymer Synthesis of N-Vinylcarbazole and Cyclohexene Oxide by Radical/Cation Transformation Polymerization

“…[44] Phenyldimethylsulfonium trifluorosulfonate (PDMS + CF 3 SO 3 -) and phenylmethylphenacylsulfonium tetrafluoroborate (PMPS + BF 4 -) were synthesized according to the literature. (45,46) Tin(IV) chloride (1.0 m solution in heptane, from Aldrich) was used as received. VCZ (extra pure, from Nacalai Tesque Inc. Japan) was recrystallized from methanol.…”