2 Synthetic methods : Part (iii) Heteroatom methods

Abstract

A particular focus this year is the synthesis of alkenes and some of their reactions. Over recent years alkene metathesis has become a, perhaps the, standard method for the synthesis of alkenes, due to the development of efficient catalysts, largely by Grubbs and Schrock, that are reasonably stable, give high turnover numbers, are tolerant of a range of functional groups and are commercially available; alkene metathesis has the great strength of being a catalytic method that is highly atom efficient, in terms of the substrate, as, in the simplest case, the only by-product is ethene, and has been applied by numerous researchers to many complex and elegant target syntheses. Selectivity is, of course, a major issue in alkene synthesis, and progress in addressing the problem of product selectivity (regio-/chemo-selectivity) in cross metathesis is being made. Nevertheless while stereoselectivity in cross metathesis, usually for E-alkenes, is often very high, and substrate influence on stereoselectivity is becoming better understood (and predictable), catalysts that yield Z- rather than E-alkenes are not yet available. However, despite the rise of alkene metathesis, the older tools in the synthetic organic chemist’s tool-box should not be discarded or forgotten: the classical heteroatom methods of alkene synthesis have life and use in them yet and continue to be developed and refined: progress with, and new variants of, these methods is discussed.