Practical Synthesis of α,α-Dibromo Esters from Aldehydes

Herein, we report an efficient and practical method for synthesizing α,α-dibromo esters, which are the precursors of ynolates, through the dibromination of aldehydes followed by oxidative esterification using iodine. Our method was successfully employed in a large-scale synthesis to yield more than 30 g of dibromo esters. These two steps can be performed in a one-pot manner, which makes the method adaptable even for aldehydes having low boiling points.

Entry into Lithium Ynolates from α,α,α-Tribromomethyl Ketones: Synthesis of Cyclobutenes via the [2 + 2] Cycloaddition with α,β-Unsaturated Carbonyls

This study reports the synthesis of cyclobutene derivatives in good yields via the [2 + 2] cycloaddition between lithium ynolates and α,β-unsaturated carbonyls. The ynolates are generated from α,α,α-tribromomethyl ketones and tert-butyl lithium via a simple and novel method, which does not produce any harmful byproducts, such as lithium alkoxide, which induces a polymerization reaction with α,β-unsaturated carbonyls.

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

Quadruple Role of Pd Catalyst in Domino Reaction Involving Aryl to Alkyl 1,5-Pd Migration to Access 1,9-Bridged Triptycenes

A Pd-catalyzed domino reaction of 1,8,13-tribromo-9-methoxytriptycenes is reported. Under conventional Suzuki coupling conditions, the triptycenes underwent multiple transformations to give 1,9-bridged triptycenes. Based on mechanistic investigations, a single Pd catalyst functions as Pd⁰ , Pd^II and Pd^IV species to catalyze four distinct processes: (1) aryl to alkyl 1,5-Pd migration, (2) intramolecular arylation, (3) homocoupling of phenylboronic acid and (4) Suzuki coupling. DFT calculations revealed that 1,5-Pd migration likely proceeds via both concerted Pd^II and stepwise Pd^IV routes. Asymmetric synthesis of the chiral triptycenes, as well as optical resolution, and further transformation are also reported.