Springer Small Ring Compounds in Organic Synthesis VI: 207 (Topics in Current Chemistry, 207)

Since the pioneering work by Sarel and co-workers on the iron carbonyl p- moted transformation of vinylcyclopropanes and related compounds [1],a - riety of transition metal complexes have been examined to achieve effective - tivation of the vinylcyclopropane-cyclopentene rearrangement which usually requires pyrolytic conditions. These reactions have been applied to natural product synthesis in some cases and have already been reviewed in several - cellent articles [2-4]. Contrary to the well-established chemistry of the vinylcyclopropanes, the corresponding reactions of alkynyl- and propadienylcyclopropanes have not, until recently,received much attention.We present here a summary of the recent efforts towards the development of transition metal promoted transformation of these molecules with a brief survey of the corresponding thermal reactions. 2 Rearrangement of Alkynylcyclopropanols Unlike the well-known chemistry of the vinylcyclopropane-cyclopentene - arrangement, there is no general method for the rearrangement of alkyn- cyclopropane to cyclopentene derivatives.One specific example is the pyrolysis of 1-ethynyl-2-methylcyclopropane to methylenecyclopentene and other c- pounds [5].At 530°C, 1-ethynyl-2-methylcyclopropane (1) undergoes a [1,- hydrogen shift to give hexa-1,2,5-triene ( 2),which further isomerizes to met- lenecyclopentenes 3 and 4 in 38 and 29% yield,respectively (Scheme 1). From the Back Cover This current and five previous volumes (Volumes 133, 135, 144, 155, 178) convincingly demonstrate the vast applications of small rings in modern Organic Synthesis. Such applications range from total syntheses of cyclopropyl-group-containing natural products and non-natural biologically active compounds or compounds with other important properties (e.g. liquid crystalline) via syntheses of cyclopropyl analogues of natural and non-natural physiologically active compounds, e.g. peptidomimetics, to the use of cyclopropyl groups as reactive subunits in so-called composite functional groups. This current volume covers a survey of the wide range of biological activities of cyclopropyl-containing compounds, up-to-date comprehensive reviews on the multiple applicabilities of two multifunctional small ring building blocks - methyl-2-chloro-2-cyclopropylidene acetate and bicyclopropylidene - in Organic Synthesis as well as a striking new approach to cyclopentenones from easily accessible 1-ethynylcyclopropanols, which is rather general and favorably complements other cyclopentenone syntheses.