Organocatalytic Asymmetric Michael Addition of Rhodanines to Azadienes for Assembling of Sulfur‐containing Tetrasubstituted Carbon Stereocenters

Abstract

The squaramide catalyzed enantioselective Michael addition of rhodanines to 2-arylidene-N-tosylbenzofuran-3(2H)-imines has been established, which enables the formation of benzofurans bearing both rhodanine and sulfur-containing tetrasubstituted stereocenter structural motif in good to high yields with good to excellent enantio-and diastereoselectivities.

Enantioselective Construction of Vicinal Sulfur‐functionalized Quaternary and Tertiary Stereocenters via Organocatalytic Michael Addition of 5H‐Thiazol‐4‐ones to 1‐Azadienes

“…Recently, we have achieved the organocatalytic enantioselective conjugate additions of thiazolones to isatin‐derived ketimines and a series of p ‐quinone methides . Inspired by Zhao's work, we have successfully developed the organocatalytic asymmetric 1,4‐conjugate addition of 2‐arylidene‐ N ‐tosylbenzofuran‐3(2 H )‐imines with rhodanines and γ‐substituted β,γ‐unsaturated γ‐lactones . Based on our previous work and as a continuation of our effort in organocatalytic asymmetric conjugate additions, we disclose here the chiral phosphoric acid catalyzed 1,4‐conjugate addition of 5 H ‐thiazol‐4‐ones to 2‐arylidene‐ N ‐tosylbenzofuran‐3(2 H )‐imines, affording a series of optically active benzofuran derivatives featured by vicinal sulfur‐containing quaternary and tertiary stereocenters (Scheme E).…”

Recent Advances in Catalytic Asymmetric Reactions of Thiazolones, Rhodanines and Their Derivatives

“…Based on our previous work on organocatalytic conjugate addition of 5H-thiazol-4-ones, we developed an asymmetric Michael addition of rhodanines 98 to 2arylidene-N-tosylbenzofuran-3(2H)-imines 99 (Scheme 28). [36] Catalyzed by quinine-based squaramide C35, reactions proceeded smoothly to furnish a wide range of benzofurans 100 bearing both rhodanine and sulfur-containing tetrasubstituted stereocenter structural motif in 81-96% yields with 82-> 98% ee and > 20:1 dr. This Michael addition not only enabled the formation of sulfur-containing tetrasubstituted stereocenter but also enriched the chemistry of both rhodanines and 2-arylidene-N-tosylbenzofuran-3(2H)imines.…”

Chiral Brønsted acid-catalyzed conjugate addition of indoles to azadienes: Enantioselective synthesis of hetero-triarylmethanes

“…Aurone-derived azadienes have been regarded as a pivotal class of highly reactive intermediates in organic synthesis due to the driving force of aromatization [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]. In the past few years, only a few catalytic asymmetric processes of azadienes have been successfully developed on the basis of transition-metal catalysis and organo-catalysis [10][11][12][13][14][15][16][17][18][19][20]. Zhao and co-workers [10][11][12] disclosed palladium-catalyzed asymmetric formal cycloaddition of azadienes to prepare medium-sized compounds including benzofuran-fused nine-membered and ten-membered heterocycles.…”

“…The enantioselective amino-acid-derived phosphine-catalyzed formal [4+4] cycloaddition of azadienes with allene ketones to afford eight-membered structural motifs has been established by Lu's group [16]. Recently, chiral Brønsted bases have been used as highly enantioselective bifunctional catalysts for the asymmetric nucleophilic addition of phosphites, thiols and rhodanines to azadienes [17][18][19]. Additionally, the formal [4+2] cycloaddition of azadienes with malononitrile using bifunctional squaramide as catalyst has been realized by our group [20] (Scheme 1a).…”