Functionalised cyclopropenes as synthetic intermediates.

Although the use of cyclopropanes in synthesis has been an area of very considerable interest for many years, much less attention has been drawn to the potential and actual uses of cyclopropenes. This may perhaps be a reflection of the perceived difficulty in handling such species, but probably also results from the rather limited routes to cyclopropenes, and in particular those bearing other functional groups, compared to the variety available which lead to the saturated analogues. However, the development of more flexible routes to cyclopropenes makes available not only the exploitation of those reactions which are peculiar to the unsaturated system but also, through stereocontrolled addition to the double bond, provides more efficient routes to cyclopropanes of particular stereochemistry. This review will attempt to identify the progress which has been made in the synthesis of cyclopropenes, to show the rich variety of their synthetic transformations, and to point to areas where future progress may occur. It will not cover purely structural or spectroscopic aspects of cyclopropene chemistry, which were dealt with in most excellent fashion by Closs 1), and in several later reviews 2). Nor will the photochemical or metal induced reactions be dealt with in great detail, the former area having been covered in reviews by Padwa3) and the latter in an article in the present series by Binger and Buch4). [ABSTRACT FROM AUTHOR]