Metal carboxylates cyclopropane ring

In cyclopropane carboxylates the ring strain influences the acidity of the a-carbon, thus the enolates are more difficult to prepare and once made, are more reactive than in the higher-inem-bered rings. These enolates probably do not have an enolate structure, but rather are a-metal-lated species. 

A few natural products which contain the cyclopropyl ring have been synthesized through metal catalysed cyclopropanation using dicarbonyl diazomethanes. ( )-Cycloeudesmol 63, isolated from marine alga Chondria oppositiclada, was synthesized via a sequence involving a copper catalysed cyclopropanation of a-diazo-/8-ketoester 61 to give the key intermediate 62 (equation 73)1 7,108. Similarly, the bicyclo[3.1.0]hexane derivative 65 was synthesized from the corresponding a-diazo-/8-ketoester 64 via the catalytic method and was converted into ( )-trinoranastreptene 66 (equation 74)109. Intramolecular cyclopropanation of -diazo-/i-ketoesters 67 results in lactones 68 which are precursors to 1-aminocyclopropane-l-carboxylic acids 69 (equation 75)110. 

Rednetive cleatage of cyclopropane rings. Cyclopropanes can be reductively cleaved by solutions of an alkali metal in liquid ammonia if a carbonyl group (example I), a carboxylate group (example 11), or a phenyl group (example 111) is attached to the cyclopropyl ring. 

Reactions of arenes carrying a coordinating substituent with alkenes may give alkylated derivatives when catalysed by ruthenium biscarboxylate complexes. Experiments with deuterium-labelled compounds indicate that carbon-hydrogen metallation is reversible, so that reductive elimination from intermediates such as (90) is rate determining. Carboxylate-assisted ruthenium catalysis also allows the reaction of 2-arylpyridines with methylenecyclopropane to give derivatives, (91), in which the cyclopropane ring is conserved. ... 

Diazomethane is also decomposed by N O)40 -43 and Pd(0) complexes43 . Electron-poor alkenes such as methyl acrylate are cyclopropanated efficiently with Ni(0) catalysts, whereas with Pd(0) yields were much lower (Scheme 1)43). Cyclopropanes derived from styrene, cyclohexene or 1-hexene were formed only in trace yields. In the uncatalyzed reaction between diazomethane and methyl acrylate, methyl 2-pyrazoline-3-carboxylate and methyl crotonate are formed competitively, but the yield of the latter can be largely reduced by adding an appropriate amount of catalyst. It has been verified that cyclopropane formation does not result from metal-catalyzed ring contraction of the 2-pyrazoline, Instead, a nickel(0)-carbene complex is assumed to be involved in the direct cyclopropanation of the olefin. The preference of such an intermediate for an electron-poor alkene is in agreement with the view that nickel carbenoids are nucleophilic 44). 

It is not known whether or not this transformation is catalyzed by the transition metal. However, the metal-catalyzed ring-opening reaction of (3-alkoxycyclopropane carboxylates yielding vinyl ethers (e.g. 50 -> 51 and 52 - 53) is well documented 97 120 . Several catalysts are suited [PtCl2 2 PhCN, Rh2(OAc)4, [Rh(CO)2Cl]2, [Ru(CO)3Cl2]2, Cu bronze, CuCl], but with all of them, reaction temperatures higher than those needed for the carbenoid cyclopropanation reaction are required. 

Although the formation of three-membered rings by cyclopropanation of olefins with metal carbenoids is commonplace, the construction of such systems via intramolecular C-H insertion is quite rare. This is because 1,2 migration of any hydride atoms a to the carbenoid center is typically very facile, rendering it inactive toward further transformations [56], It was found, however, that [i-tosyl a-diazo carbonyl compounds 37 are suitable substrates for intramolecular 1,3 C-H insertion reactions catalyzed by achiral rhodium carboxylates 25 (Scheme 6) [57],... 

Then the carboxylic acid was converted (via the acid chloride) to the diazoketone (Chapter 9), and decomposition of the latter via the carbene and insertion produced the substituted cyclopropane. Next, the keto group was converted to a methylene unit via the Wittig, and thermolysis generated the third cyclopentyl ring. Dissolving metal reduction and epimerization in sodium ethoxide set the stage for conversion of the ester to an alkyl group. 

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