Iron-Catalyzed Cyclization of Alkynols with Diorganyl Diselenides: Synthesis of 2,5-Dihydrofuran, 3,6-Dihydro-2H-pyran, and 2,5-Dihydro-1H-pyrrole Organoselanyl Derivatives.

An iron-catalyzed system, using diorganyl diselenides as an organoselenium source, was used for the cyclization of 1,4-butyne-diols in the preparation of 3,4-bis(organoselanyl)-2,5-dihydrofurans. The optimized reaction conditions are compatible with many functional groups in 1,4-butyne-diols and diorganyl diselenides. In addition, this catalyst system was also efficient with diorganyl disulfides, but it did not work for diorganyl ditellurides. The same reaction conditions were also extended to pentyne-1,5-diol for the preparation of 4,5-bis(organoselanyl)-3,6-dihydro-2H-pyrans and to 4-amino-butynol for the preparation of 2,5-dihydro-1H-pyrrole derivatives. The synthetic utility of these heterocycles was studied using 5-bis(organoselanyl)-3,6-dihydro-2H-pyrans as substrate in a Kumada-type cross-coupling reaction.