Ir-Catalyzed Asymmetric Total Syntheses of Bisdehydrotuberostemonine D, Putative Bisdehydrotuberostemonine E and Structural Revision of the Latter

The first total syntheses of bisdehydrotuberostemonine D (8) and putative bisdehydrotuberostemonine E (9), two novel pyrrole Stemona alkaloids, along with the synthesis of bisdehydrotuberostemonine (3) have been completed in 12-13 steps. Our strategy harnesses the power of transition-metal-catalyzed reactions employing Ir, Ru, and Pd, in particular Ir-catalyzed asymmetric allylation of aldehydes, two distinct protocols recently developed by Carreira and Krische, respectively. The threefold use of Ir catalysis, first in the stereodivergent construction of two contiguous stereocenters at C (9,10) and then in rapid formation of the two γ-butyrolactone motifs, enabled the route's efficiency. Through this work, the originally assigned structure of bisdehydrotuberostemonine E (9) should be revised as 18α-bisdehydrotuberostemonine D (8*).

Cycloaddition Initiated by Ynolates: High-Energy Dianion Equivalents as a Molecular Glue

In this paper, ynolate-initiated cycloaddition (annulation) to form a range of carbocycles and heterocycles is described. Ynolates consist of a ketene anion equivalent, which contains both nucleophilic and electrophilic moieties, and a carbodianion equivalent that achieves double addition. Hence, in addition to the usual [n+2] cycloaddition, ynolates can perform formal [n+1]-type annulations. Their high-energy performance has been demonstrated by their triple addition to arynes to generate triptycenes, in which the C–C triple bond of ynolates is cleaved. The synthetic applications of these methods, including natural products synthesis, are also described.

1 Introduction

2 Preparation of Ynolates

2.1 Double Lithiation

2.2 Flow Synthesis

2.3 Double Deprotonation

3 [2+2] Cycloaddition to C=O Bond

3.1 To Aldehydes and Ketones

3.2 Sequential Cycloaddition

4 [2+2] Cycloaddition to Imino Groups

Synthetic Studies toward Parvistemoline Using Asymmetric Ir/Amine-Catalyzed Allylation

The common, key tricyclic core of stemona alkaloids parvistemonine (1) and parvistemoline (2), whose synthetic efforts have not reported yet, was constructed through a new strategy in which three contiguous stereogenic centers were set by using Carreira's asymmetric Ir/amine-catalyzed allylation of aldehyde with α-vinylfurfuryl alcohol and Ellman's sulfinamide chiral auxiliary, respectively. The furan ring was especially designed to act as the precursor of the butyrolactone while establishing the significant chirality.