Stereocontrolled Total Synthesis of theStemona Alkaloid (−)-Stenine

Abstract

The Stemona alkaloid stenine (1), isolated from Stemona tuberosa of physiologically active stemonaceous plants, possesses the structurally novel and unique azepinoindole skeleton (B,C,D-ring system). We have achieved the asymmetric total synthesis of (-)-stenine (1), starting from 1,5-pentanediol (10). The key features are an intramolecular diastereoselective Diels-Alder reaction of the (E,E,E) triene 6, prepared in a convergent fashion from three components--dienyl chloride 7, dithiane 8, and chiral phosphonate 9--and efficient construction of the tricyclic A,B,D-ring system 29 through thermodynamically controlled regioselective enolization of the bicyclic ketone 25. In this article, we describe in detail the highly stereocontrolled total synthesis of (-)-stenine (1). These results should be useful for the asymmetric total synthesis of another, more complex. molecule: tuberostemonine (2), the synthesis of which has never been reported.

Total Synthesis, Stereochemical Reassignment, and Biological Evaluation of (−)‐Lyngbyaloside B

“…Protection of 11 as its p-methoxybenzylidene acetal and DIBALH reduction [16] led to alcohol 12, which was oxidized [17] to give aldehyde 6. Building block 7 was synthesized from aldehyde 13 [18] in six steps (Scheme 3). Brown asymmetric crotylation [19] of 13 (77 %, e.r.…”

Studies toward the Total Synthesis of Gambieric Acids A and C: Convergent Assembly of the Nonacyclic Polyether Skeleton

“…Diol 43 was converted in a further three steps into the primary alcohol 44 , which was in turn converted into the terminal alkene 45 by the method developed by Grieco, Gilman, and Nishizawa 20. The TIPS and acetonide groups in 45 were exchanged for benzyl protecting groups, and the PMB group was removed selectively21 to complete the synthesis of the desired GHIJ‐ring fragment 7 .…”

A Rapid Stereocontrolled Entry to the ABCD Tetracyclic Core of Neotuberostemonine

“…A number of syntheses of 2 have now been reported reported since the first successful total synthesis by Hart and Chen,3 and include contributions from the groups of Wipf,4 Morimoto,5 and Padwa 6. Morimoto et al7 have described a full account of their total synthesis of 2 , from which they aim to develop a strategy towards 3 . Very recently, Wipf et al8 described the first total synthesis of 3 .…”