Synthesis of functionalized indoles by Diels-Alder reaction utilizing the diene generated by the alkylation of N-methyl-3-thioacetylpyrrole.

The Electronic Spectrum of the Fulvenallenyl Radical

“…To the best of our knowledge, only four reports of 3‐vinylpyrroles being used in Diels‐Alder reactions exist [8, 9, 11, 12]. Jones et al .…”

Access to Indoles via Diels-Alder Reactions of 5-Methylthio-2-vinylpyrroles with Maleimides

“…In the only example found of Diels–Alder reactions of vinylpyrroles having an alkylthio‐substituted vinyl group, Murase et al . showed that the corresponding 3‐(1‐benzylthio)vinylpyrrole gave the Diels–Alder adduct with DMAD in 31% yield; surprisingly, the yields we achieved in our work with Diels–Alder reactions of the comparatively deactivated N ‐toluenesulfonyl‐3‐vinylpyrrole with maleimides were much higher . The poor yields in the pyrrole case of Murase et al .…”

“…Although N ‐H‐acetylpyrrole 38 was a crystalline solid that could be recrystallized for facile purification, N ‐methylacetylpyrrole 39 was a liquid that on TLC showed several closely spotting impurities; two fractional vacuum distillations gave 39 in a purity of approximately 7:1 by mass. 2‐Acetyl‐5‐methylthiopyrroles 38 and 39 were then treated with Lawesson's reagent , giving N ‐H‐ and N ‐methyl‐ 2‐acetyl‐5‐methylthiopyrroles 40 and 41 .…”

“…A mixture of the vinylpyrroles 42 and 43 [2.919 mmol, generated freshly from 2‐methylthio‐5‐thioacetyl‐1 H ‐pyrrole 40 (500 mg), approximately 1:2 42 : 43 by mass ], and the maleimide 16 (1.1 equiv) in chloroform was stirred at RT for 3 d and then refluxed for 5 h. The solvent was removed using a rotating evaporator. The crude adduct was purified by MPLC using ethyl acetate/hexanes as eluent, followed by recrystallization from methylene chloride/petroleum ether, giving 44 (405 mg, 38%) as a white powder: mp 136–137°C; 1 H NMR (300 MHz, CDCl 3 , δ) 7.25 (d, J = 8.7 Hz, 2H, Ph), 7.19 (d, J = 8.7 Hz, 2H, Ph), 6.50 (s, 1H, 7‐H), 4.13 (d, J = 9.3 Hz, 1H, 8bα‐H), 4.07 (dd, J = 3.9, 2.4 Hz, 1H, 5α‐H), 3.65 (s, 3H, 6‐Me), 3.33 (ddd, J = 9.2, 7.1, 2.0 Hz, 1H, 3aα‐H), 3.03 (ddd, J = 14.6, 2.0, 2.0 Hz, 1H, 4β‐H), 2.65 (q, J = 7.6 Hz, 2H, C H 2 CH 3 ), 2.27 (s, 3H, MeS), 2.18 (s, 3H, MeS), 2.16 (ddd, J = 14.7, 6.9, 3.9 Hz, 1H, 4α‐H), 1.22 (t, J = 7.7 Hz, 3H, CH 2 C H 3 ); 13 C NMR (75 MHz, CDCl 3 , δ) 179.5, 177.3, 145.2, 130.7, 129.9, 129.2, 127.0, 125.9, 114.6, 112.7, 39.6, 38.4, 38.2, 30.5, 29.3, 26.4, 21.4, 16.13, 16.11; IR (KBr, cm −1 ) 2965(m), 2916(m), 1775(w), 1705(s), 1514(m), 1444(m), 1432(m), 1395(m), 1347(w), 1309(w), 1296(w), 1258(w), 1216(m), 1191(m), 1139(w), 1109(w), 960(w), 870(w), 837(w), 817(m), 789(w), 761(w); HRMS m/z (M + Na + ) calcd 423.1172, found 423.1187.…”

Five‐Membered Heterocycles: Pyrrole and Related Systems

“…Similar reactions yielding isomeric adducts were performed using 1-(phenylsulfonyl)-2-vinylpyrrole [525]. Other related indole syntheses encompass the use of silyl enol ethers of 2-acylpyrroles [526,527], or a diene generated by S-alkylation of 1-methyl-3-thioacetylpyrrole [528] as the 4p-components. It is also noteworthy that some sterically hindered N-substituted 2-vinylpyrroles give mainly Michael-type addition at C5, as the required cisoid conformation is disrupted by steric interaction between the group at the pyrrole nitrogen and the substituted vinyl moiety [529].…”