Alkylation of benzoyl and furoylthioureas as polydentate systems

A study of the behaviour towards alkylation of a series of benzoyl and furo ylthioureas with 3,3-disubstitution has been carried out using NMR determin ations. X-Ray data and semiempirical theoretical calculations demonstrated that the most stable conformation for these molecules is the so-called quas i-S. Also an explanation of the high selectivity towards the S-alkylation o f these systems, based on the high contribution of the sulphur atom to the HOMO in acylthioureas is given for the title compounds. Steric factors are responsible for the difference between the percentages obtained for the S-a lkylated product in 1-(4-methylbenzoyl)-3,3-diethylthiourea and 1-benzoyl-3 ,3-dibenzylthiourea. (C) 2000 Elsevier Science Ltd All rights reserved.