Transformation of Sulfide Linkages to Carbon-Carbon Double Bond. Syntheses of cis- and trans-15,16-Dimethyldihydropyrene and Trans-15,16-Dihydropyrene

Abstract

It is shown that the transformation of sulfide linkages to carbon-carbon double bonds in highly strained molecules can be effected conveniently and in high yield by a reaction sequence of a Stevens rearrangement followed by a Hofmann elimination. This route is of particular advantage for preparing cyclophane derivatives since the medium-sized ring sulfides required as starting materials are easy to prepare. When m-xylylene dibromide is treated with 1,3-bis(mercaptomethyl)benzene, 2,11-dithia[3.3]metacyclophane (25) is formed in 80% yield. Similarly, 2,6-bis(bromomethyl)toluene (5) can be converted to 2,11-dithia-9,19-dimethyl[3.3]metacyclophane, which exists in both the syn and anti conformations (7 and 8). Subjection of these three 2,11-dithia[3.3]metacyclophane derivatives to the Stevens rearrangement leads in each case to the corresponding ring-contracted bis(methylthio)- [2.2]cyclophane, isolated as a mixture of isomers. When the mixture of isomers 10, resulting from the anti-9,18-dimethyl derivative, is subjected to a Hofmann elimination, trans-15,16-dimethyldihydropyrene (14) forms in excellent overall yield. Similarly, the mixture of isomers 18 from the syn-8,16-dimethyl derivative is converted to cis-15,16-dimethyldihydropyrene (21). Surprisingly, the Hofmann elimination reaction with the parent bis(methylthiomethyl)[ 2.2]metacyclophane (26) gives anti-[2.2]metacyclophane-1,9-diene (31), rather than the expected zrsns-15,16-dihydropyrene. Although anti-[2.2]metacyclophane-1,9-diene (31) is a stable compound and does not undergo spontaneous valence tautomerization, it is converted on irradiation to trans-15,16-dihydropyrene (35). Some of the physical and chemical properties of these bridged [14]annulenes are presented. © 1974, American Chemical Society. All rights reserved.