Anthranoxides as Highly Reactive Arynophiles for the Synthesis of Triptycenes

Mechanism and the Origins of Periselectivity in Cycloaddition Reactions of Benzyne with Dienes

Density functional theory calculations have been used to explore the reaction mechanism of (4 + 2) and (2 + 2) cycloadditions of benzyne with classical dienes. The results indicate the following: (1) (4 + 2) products arise via concerted pathways, (2) (2 + 2) products arise via stepwise pathways with diradical intermediates, and (3) these diradical intermediates are formed via isomerization of carbene intermediates. The origins of periselectivity in these reactions are analyzed using distortion/interaction analysis for the key steps, and they indicate that the tiny distortion in the very early [4 + 2] transition structure, coupled with an entropic favorability, controls selective (4 + 2) cycloaddition.

3-Trifluoromethylbenzyne: Precise Orientation in Cycloaddition Reaction Enabled Regioselective Synthesis of Trifluoromethylated Triptycenes

The first regioselective addition reactions to 3-trifluoromethylbenzyne are reported. Triple cycloaddition of ynolates to the benzyne provided 1,8,13-tris(trifluoromethyl)triptycenes with high regioselectivity. 1-Trifluoromethyltriptycenes were regioselectively obtained by the Diels–Alder reaction of anthranoxides with the benzyne. These selectivities are attributed to the electron-acceptor nature of the trifluoromethyl group on the benzyne.

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