A novel application of 2-silylated 1,3-dithiolanes for the synthesis of aryl/hetaryl-substituted ethenes and dibenzofulvenes.

Grzegorz Mlostoń,Róża Hamera-Fałdyga,Paulina Pipiak,Heinz Heimgartner

doi:10.3762/bjoc.13.185

Grzegorz Mlostoń, Róża Hamera-Fałdyga + Show 2 more

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https://doi.org/10.3762/bjoc.13.185

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Abstract

Trimethylsilyldiazomethane (TMS-CHN2) reacts readily with hetaryl thioketones to give sterically crowded 2-trimethylsilyl-4,4,5,5-tetrahetaryl-1,3-dithiolanes with complete regioselectivity at −75 °C as well as at rt. Thiofluorenone, a relatively stable and highly reactive aryl thioketone, yields upon treatment with TMS-CHN2 at −60 °C the corresponding 1,3,4-thiadiazoline. This unstable cycloadduct undergoes decomposition at ca. −45 °C and the silylated thiocarbonyl S-methanide generated thereby is trapped with complete regioselectivity by aryl or hetaryl thioketones forming also sterically crowded 2-trimethylsilyl-1,3-dithiolanes. The obtained 1,3-dithiolanes, by treatment with an equimolar amount of TBAF in a one-pot procedure, are converted in high yields into hetaryl/aryl-substituted ethenes or dibenzofulvenes, respectively, via a cycloreversion reaction of the intermediate 1,3-dithiolane carbanion. The presented protocol offers a new, highly efficient approach to tetrasubstituted ethenes and dibenzofulvenes bearing aryl and/or hetaryl substituents.

Highlights

Aryl and hetaryl-substituted ethenes form an important class of organic compounds with a growing number of applications in materials chemistry, crystal engineering, photooptics, etc
We described a different behaviour of thiofluorenone (1c), which reacted with TMS-CHN2 at −60 °C to yield the expected [3 + 2]-cycloadduct 8, which only at ca. −40 °C extruded N2 [23]
The presented study showed that 2-trimethylsilyl-4,4,5,5tetraaryl-1,3-dithiolanes, readily available by treatment of hetaryl thioketones with trimethylsilyl diazomethane (TMSCHN2), are superior substrates for the preparation of tetraarylethenes

Summary

Introduction

Aryl and hetaryl-substituted ethenes form an important class of organic compounds with a growing number of applications in materials chemistry, crystal engineering, photooptics, etc. The thiophen-2-yl-substituted ethenes [1,2,3,4,5] as well as dibenzofulvenes-containing compounds [6,7,8,9] are of special interest. As a general method for the preparation of tetrasubstituted ethenes, the McMurry reaction is widely applied [14]. Another approach, which opens access to diverse ethenes, is the ‘two-fold extrusion reaction’, which comprises the Beilstein J.

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