Free Radical Cyclization of N-Arylacrylamides: Mild and Facile Synthesis of 3-Thiocyanato Oxindoles

Abstract

A novel and convenient oxidative radical cyclization of N-substituted N-arylacrylamides for the synthesis of 3-thiocyanated oxindoles has been developed by using AgSCN and K2S2O8 as the radical source. This process allows a consistent and convenient access to SCN-containing heterocycles bearing a broad range of functional groups in good to excellent yields (up to 91%). Moreover, the use of inexpensive and readily available starting materials, operational simplicity, and excellent functional group tolerance makes this protocol practically attractive.

Organocatalyzed Asymmetric α-Thiocyanation of Oxindoles: Synthesis of Chiral Tertiary 3-Thiocyanatoxindoles

“…Furthermore, many bioactive thiocyanate-containing natural products have been verified, such as psammaplin B, welwitindolinone C (Scheme a) . Much effort has been devoted to develop various approaches for the synthesis of thiocyanates. − However, most of these achievements focused on achiral SCN-containing compounds, especially building the C­(sp 3 )–SCN bond . The efficient methods for the enantioselective introduction of the SCN group to biologically active frameworks remain rare.…”

Recent advances in radical thiocyanation cyclization or spirocyclization reactions

“…In 2018, the Feng group also developed an Ag/pyridine co-mediated oxidative arylthiocyanation of activated alkenes, which resulted in a variety of SCN-containing oxindoles (Scheme 8). 14 In comparison to the excellent work of Chen, 13 this reaction system also could undergo a smooth reaction at 75 °C with the help of 0.2 equiv. pyridine as the base.…”

“…In 2018, the Chen group first reported a radical cyclization of N -arylacrylamides with silver thiocyanate (AgSCN) to give 3-thiocyanato oxindoles with broad substrate scopes (Scheme 6). 13 With the best conditions in hand, the substituent effect of N -arylacrylamides was examined, respectively. First, methyl, benzyl, and ethyl propionate groups on the N -moiety showed that raw materials could react smoothly with AgSCN to give various final products 13–15 in moderate-to-good yields.…”

Syntheses of 3,3-Disubstituted Dihydrobenzofurans, Indolines, Indolinones and Isochromanes by Palladium-Catalyzed Tandem Reaction Using Pd(PPh3)2Cl2/(±)-BINAP as a Catalytic System

“…The domino reactions of the synthesis of them were summarized mainly as follows: (i) the Pd or Ni-catalyzed cyclocarbopalladation/coupling fractions, in which the process was initiated by Heck cyclization of a starter (halide) and a relay (alkene), followed by intermolecular coupling reactions with a terminator (organometallic reagents, alkenes, alkynes, etc. ), including Suzuki, Stille, Heck, Sonogashira, C-H activation, carbonylation and amination and so forth [15][16][17]22,24,25,[29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44]; (ii) the C-H oxidative radical coupling reactions, in which these transformations were based on tandem radical addition/cyclization in the presence of oxidants with/without metal catalysts [18][19][20][21]23,26,[45][46][47][48][49][50][51][52][53][54][55]; and (iii) the other reactions [24,[56][57][58][5...…”