ALKYLATION OF AROMATICS WITH DIOLS IN SUPERACIDIC MEDIA

Friedel-Crafts alkylation of simple aromatics (benzene, toluene, o-, m - and p-xylene) with various types of diols in the presence of superac idic trifluoromethanesulfonic acid was studied. 1,2- and 1,3-diols wer e found to bring about only monoalkylation yielding unusual monoalkyla ted products: bis(1-methyl-2-phenylpropyl) ether was formed in the rea ction of 2,3-butanediol, and 2,4-dimethyl-2,4-pentanediol produced mon o- and di-tert-butyl-substituted benzenes. Higher diol homologues, in turn, undergo electrophilic cyclialkylative ring closure (cyclialkylat ion) to form tetralin derivatives with high selectivities and in good yields. Additional primary alkylation processes are monoalkylation to yield alkylbenzenes and the formation of diphenylalkanes. The products thus formed may participate in secondary transformations, which are a second cyclialkylation (formation of octahydroanthracene and -phenant hrene derivatives), isomerization and dehydrogenation. Mechanistic stu dies with stereoisomeric 2,5-hexanediols point to the involvement of o pen dicationic intermediates in the alkylation process.