Synthesis of Ynolates via Double Deprotonation of Nonbrominated Esters

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.

n-Butyllithium-Induced Tandem [3,3]-Sigmatropic Rearrangement and Carbonyl Olefination of Allyl-1,1-dichlorovinyl Ethers

Exposure of dichlorovinyl ethers 1 to n-butyllithium and addition of saturated or unsaturated aldehydes, ketones, or esters at ambient temperature furnishes rearranged α,β-unsaturated carboxylic acids, isolated as their corresponding methyl esters 2 in 48-91% overall yields. Exposure of dichlorovinyl ethers 1 to n-butyllithium, addition of aldehydes, ketones, dialdehydes, or diketones at -78 °C, and warming to 80 °C in the presence of SiO₂ provide 1,4-dienes 3 or cycloalken-1-ols (or their dehydration products) 4 in 45-72% overall yields.

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

Anthranoxides as Highly Reactive Arynophiles for the Synthesis of Triptycenes

We report herein an efficient method to synthesize triptycenes by the reaction of benzynes and anthranoxides, which are electron-rich and readily prepared from the corresponding anthrones. Using this method, 1,9-syn-substituted triptycenes were regioselectively obtained employing 3-methoxybenzynes. This method was also applied to synthesize pentiptycenes. A DFT study revealed that the cycloaddition of lithium anthranoxide and benzyne proceeds stepwise.