Cyclopropanes rhodium-catalyzed ring-opening

Rhodium-catalyzed ring-opening isomerization and hydrogenation of [ (diphenylphosphino)oxy methyl]cyclopropane (1) formed linear products via cleavage of the C1-C2 bond by assistance of a chelating phosphine group (Scheme 2.2) [5]. 

Palladium-catalyzed ring-opening hydrosilylation of cyclopropyl ketones formed (Z)-enol silanes (Scheme 2.79) [131]. The mechanism is proposed to proceed via oxidative cyclization, ring contraction, transmetalation, and reductive elimination. In contrast, the rhodium-catalyzed reaction afforded mixtures of cyclopropanes and ring-opened products [132]. 

The diastereoselective and enantioselective preparation of cyclopropanes has attracted attention since chiral cyclopropanes were found to occur in many natural products [11]. Moreover, cyclopropanes are useful intermediates in organic synthesis. There are many methods of cyclopropane ring opening that transfer stereochemical information from the substrate to acyclic products in a stereocontrolled manner [12]. Among the methods used for the preparation of cyclopropanes from olehns, the Simmons-Smith and related reactions as well as reactions of diazoalkanes catalyzed by rhodium, copper and cobalt salts have frequently been applied [13]. The preparatively simple Makosza reaction [14] has scarcely been used. 

The rhodium- or copper-catalyzed cyclopropanation of furan and its derivatives with diazo-acetic esters,300-302 or ethyl 2-diazopropanoate300 usually leads to a mixture of the 2-oxa-bicyclo[3.1.0]hex-3-ene-e co-6-carboxylate, ring-opened (4Z)-6-oxohexa-2,4-dienoates, and ring-substituted furans. Only with electron-deficient furans methyl furan-2-carboxylates, 2-[( )-2-methoxycarbonylvinyl]furan300 and with benzofuran,301,303 was the cyclopropane product obtained exclusively. Examples 37-40 are representative.300... 

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