HELVLTICA CHIMI( zyxwvu A AC~A zyxwvu - zyxwv Voi. 64, Fasc. 2 (1981) - Nr. 39 3x9 39. Studies on the Conversions of Diols and Cyclic Ethers Part 48') Dehydration of Alcohols and Diols on the Action of Dimethylsulfoxide by Arpad Molnlr and Mihily Bart6k2) Department of Organic Chemistry, Jozsef Attila University, Dom tCr 8, H-6720 Szeged. Hungary (20.XI. 80) zyxwvu Summary The transformations of 13 alcohols and 13 diols in the presence of a small amount dimethylsulfoxide zyxwvu (1/16 mol) were studied. Relationships were found be- tween the type of the hydroxy compound and the selectivity of the transformation, and conclusions were drawn regarding the transformation mechanism. The ether formation observed with certain alcohols proceeds via a carbenium cation. The reaction conditions applied were found suitable for inducing water elimination from the ditertiary 1,2- and 1,3-diols (pinacol rearrangement, 1,2-elimination). From the 1,4- and 1,5-diols the corresponding oxacycloalkanes can be obtained in good yield. Cyclodehydration occurs by intramolecular nucleophilic substitution, via a concerted mechanism. The effect of DMSO is exerted directly, and proton- catalysis occurs simultaneously. 1. Introduction. - During the past twenty years a number of publications have appeared on the transformations of diols on the action of dimethylsulfoxide (DMSO) (see, for example, review [2]). The transformations of 1,2- and 1,3-diols lead not only to the formation of dienes, 0x0 compounds and unsaturated alcohols [3], but in certain cases to dioxacycloalkanes [4] [5]. For the higher diol homologues the main reaction is cyclodehydration to the cyclic ether [3] [6- 101, generally with good yield, but side-reactions (diene formation) sometimes accom- pany this process. It is a common feature of these investigations that the reagent was used in large excess, the diol: DMSO ratio usually lying in the range 1 : 4- 1 : 19. It has recently been demonstrated in the transformations of various benzyl alcohols [ l l ] that at very high alcohol: DMSO ratios (16:l) the olefin formation and certain oxidation reactions to be observed when the reagent is in high excess over the alcohol can be totally suppressed, and ethers can be obtained in excellent yields. ~ I) Part 47: [I]. 2, Author, to whom the correspondence should be addressed 0018-019X/81/2/0389-10$01.00/0 zyxwvu 0 1981 Schweizerische Chemische Gesellschaft