Generation and Cycloaddition of o-Quinodimethane in Aqueous Medium

Lothar W Bieber,Margarete F Da Silva

doi:10.3390/60500472

Lothar W Bieber, Margarete F Da Silva

Open Access

https://doi.org/10.3390/60500472

Copy DOI

Abstract

o-Quinodimethane can be generated from α,α'-dihalo-o-xylenes using zinc in aqueous solution. In the presence of activated dienophiles cycloadducts can be obtained directly. Catalysis with tris-triphenylphosphine ruthenium(II) dichloride reduces side reactions such as reduction and polymerisation and improves the yield. This is the first example of an organometallic cyclisation in aqueous medium using dihalo compounds.

Highlights

Introduction o-Quinodimethanes (o-xylylenes) are reactive intermediates widely used for the synthesis of polycyclic compounds via inter- or intramolecular Diels-Alder reactions [1]
The reaction of the dibromo compound 1a with zinc dust in saturated aqueous ammonium chloride was complete in a few minutes at r.t. and produced a polymeric material 3 containing 67 % of C-C coupled methylene groups and 28 % of methyl groups as a result of reduction; only trace amounts of o-xylene and dimeric or trimeric coupling products, but no 2 at all could be detected by GC/MS (Table 1, entry 1)
These results agree rather well with those obtained by Alder under anhydrous conditions in DMF [6]

Summary

Introduction

Introduction oQuinodimethanes (o-xylylenes) are reactive intermediates widely used for the synthesis of polycyclic compounds via inter- or intramolecular Diels-Alder reactions [1]. Recent progress in aqueous Diels-Alder cycloadditions and organometallic reactions [3], especially the successful Wurtz coupling of benzylic halides [4] and their Barbier addition to carbonyl compounds [5], prompted us to study the behaviour of α,α'-dihalo-o-xylenes (1) under similar conditions in the hope to obtain benzocyclobutene (2) or, in the presence of dienophiles, cycloadducts of o-quinodimethane.

Results

Conclusion