Carbonyl-substituted cyclopropanes

Catalytic hydrogenation will usually open the less hindered bond adjacent to the carbonyl-substituted cyclopropane carbon Therefore, construction of the sinularene skeleton has become possible (cleavage of bond a) on the other hand, Cr(II) breaks the more shielded C-C bond (cleavage of bond b) in a very similar compound yielding the longifolene system (equation 34) . 

The first report on the reduction of a carbonyl substituted cyclopropane was published in 1949. Reactions of methyl cyclopropyl ketone (131) with sodium in liquid ammonia in the presence of ammonium sulfate yielded instead of the expected methyl cyclopropylcarbinol (132) only a mixture of 2-pentanone (133) and 2-pentanol (134). 

Phenyl, vinyl or carbonyl substituted cyclopropanes are more easily hydrogenolyzed than are the alkyl substituted species. Such compounds are commonly cleaved over palladium catalysts at room temperature and atmospheric pressure. Hydrogenolyses run over platinum, rhodium or nickel catalysts frequently result in the saturation of the double bond, the benzene ring or the carbonyl group with the cyclopropane ring remaining intact or cleaved to only a slight extent. 20 As illustrated in Fig. 20.22 the bond broken in the... 

Carbanions or ylides have also been employed as formal carbene sources for the stereoselective construction of carbonyl-substituted cyclopropane derivatives. The McCoy reaction30 of the enolate from methyl chloroacetate with methyl propenoate in toluene provides a 70 30 mixture of dimethyl cisitransA, 2-cyclopropanedicarboxylate31. These stereoisomers can be separated by fractional distillation. 

The last group of reactions uses ring opening of carbonyl or 1-hydroxyalkyl substituted cyclopropanes, which operate as a -synthons. d -Synthons, e.g. hydroxide or halides, yield 1,4-disubstituted products (E. Wenkert, 1970 A). (1-Hydroxyalkyl)- and (1-haloalkyl)-cyclopropanes are rearranged to homoallylic halides, e.g. in Julia s method of terpene synthesis (M. Julia, 1961, 1974 S.F. Brady, I968 J.P. McCormick, 1975). 

Salaiin, J. R. Y. Synthesis and Synthetic Applications of 1-Donor Substituted Cyclopropanes with Ethynvl, Vinyl and Carbonyl Groups, 144, 1-71 (1987). 

The [Rh(CO)2Cl]2-induced ring fission of substituted cyclopropanes 8a-b affords the rhodium complexes 9a-b via carbonylation [8]. The regioselectivity of carbonyl group insertion depends on the substituent. Reduction with NaBH4 leads to the corresponding alcohol. (Scheme 4)... 

A diene system with unsymmetrical 1,4-disubstitution is converted to the iron carbonyl complex 1 which is resolved into its enantiomers. The aldehyde function is conformationally locked in the transoid position and is diastereofacially shielded from the bottom face. Nucleophiles attack from the top face with high selectivity. Alternatively, chain elongation leads to the triene 2 which is reacted with diazomethane. Cerium(IV) oxidation removes the metal and furnishes the substituted cyclopropane 3. 

Functionalized zinc carbenoids have been prepared from carbonyl compounds by an indirect strategy. The deoxygenation of a carbonyl compound to an organozinc carbenoid can be induced by a reaction with zinc and TMSCl. Therefore, the aldehyde or ketone, when treated with TMSCl or l,2-bis(chlorodimethylsilyl)ethane in the presence of an alkene, generates the cyclopropanation product. This method is quite effective for the production of alkoxy-substituted cyclopropane derivatives. A 55% yield of the... 

We acknowledge that methylcyclopropane is no less a substituted cyclopropane as is methyl cyclopropanecarboxylate. However, for the former species we use the hydrocarbon equation 3 with nc = 4, and for the latter species we use the substituted compound equation 4 with b = 10.5 (for esters) and flc = 5 (remember the carbonyl carbon in calculating the number of nonquaternary carbons). 

From the three direct [2 + l]-cycIoaddition routes, path a employing electronrich olefins and acceptor-substituted carbenes is the most efficient one, since the alkenes can be synthesized from carbonyl compounds or other precursors and the carbenes are produced from easily available diazo alkanes. Therefore this very flexible mode to construct donor-acceptor substituted cyclopropanes is by far the most frequently used route. 

The synthesis of cyclopropanes from carbonyl compounds represents a new approach for converting zirconacycles into carbocycles via a deoxygenative ring contraction under Lewis acid activation. It differs in that from the spontaneous Kulinkovich process. Further progress would involve extension to the synthesis of 1,2-substituted cyclopropanes and the development of catalytic and enantioselective variants. 

J. S. Chickos, D. G. Hesse, J. F. Liebman and S. Y. Panshin, J. Org. Chem., 53, 3435 (1988). In the absence of a literature value suggested for a desired enthalpy of vaporization for a substituted hydrocarbon, this CHLP protocol will be used implicitly to estimate the desired quantity. We acknowledge that methylcyclopropane is no less a substituted cyclopropane as is methyl cyclopropanecarboxylate. However, for the former species we use the hydrocarbon equation 3 with Pic = 4, and for the latter species we use the substituted compound equation 4 with Z = 10.5 (for esters) and fic= 5 (remember the carbonyl carbon in calculating the number of nonquaternary carbons). 

As is the case for oxycyclopropanes extra activation and extended product functionality is achieved by using sulphur-substituted cyclopropanes with a vicinal acceptor group. According to equation 116 synthesis of a variety of y-oxothioesters and j -oxoketene dithioacetals is possible. A formylcyclopropane of this type has been converted to a furan derivative " . Transformation of the carbonyl to a hydroxymethyl group and acid treatment allows preparation of dienes " ... 

Preparation of alkylidene cyclopropanes is feasible by alkylation of lithium carbenoids followed by base-promoted elimination (equation 13or by addition of carbonyl compounds, silylation and reductive elimination (equation 132). Similarities with the chemistry displayed by sulphur-substituted cyclopropanes (Section VI.D.l) are obvious. 

The interaction of the complex tetracarbonyldi-fj-chlorodirhodium with cyclopropane and substituted cyclopropanes produced complexes 3 and 4a, ° respectively, with the same dimeric structure. Contrary to the reaction with the platinum complex a five-membered ring 3 or 4120 jjj which both the metal and the carbon of one of the carbonyl groups were incorporated was formed. The cleavage site was the least substituted C —C bond. Analogous products 4c and 4b (75%) were obtained with bicyclo[4.1.0]heptane and phenylcyclopropane, respective-... 

Table 5. jS-Amino Esters and y-Phenyl Carbonyl Compounds by Ring-Opening Reactions of Oxygen-Substituted Cyclopropanes with Nitrenes and Carbenes... 

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