Additionsreaktionen zwischen lsocyaniden und Doppelbin-dungssystemen

A review is made of the recently discovered BF₃-catalyzed as well as other addition reactions between isocyanides and double-bond systems such as C O, C - N, N = O, etc. These additions generally involve the reaction of three molecules. A reaction of type I, characterized by the addition of two isocyanide molecules to one double bond, give rise to four-membered cyclic compounds. These primary reaction products may in many cases be isolated or may be readily converted to other products in which ringopening or rearrangement to five-membered heterocycles has occured:. A second type of reaction (II), characterized by the addition of one isocyanide molecule to two double bonds, affords five-membered heterocycles:. The formation of larger rings is seldom observed although it is in principle possible. Substituent effects and the conditions under which the reaction is carried out determine which reaction path is followed. Both types of addition reaction (I and II) can occur with the same double-bond system. In contrast to the Passerini and Ugi reactions, the cycloaddition reactions surveyed in this review are carried out in aprotic medium.