Arenes cyclopropanation

The Buchner reaction can be shut down by arene chromium tricarbonyl complexation " Thus benezenechromium tricarbonyl 95 and even electron-rich para-dimethoxybenzenechromium tricarbonyl (structure not shown) fail to react with ethyl diazoacetate and rhodium(II) trifluoroacetate. In contrast, the same reaction with benzene provides a single isomer of the cycloheptatriene in 98% yield. The Buchner reaction of pseudo-Ci symmetric substrate 97 clearly demonstrates the effect of chromium tricarbonyl complexation on arene cyclopropanation. Decomposition of diazoacetamide 97 with rhodium(II) acetate brings about exclusive addition... 

Alkenes, alkynes, arenes, cyclopropanes Carbon monoxide CO Isonitriles R—N C Carbanions, CN, RC C ... 

Abstract The photoinduced reactions of metal carbene complexes, particularly Group 6 Fischer carbenes, are comprehensively presented in this chapter with a complete listing of published examples. A majority of these processes involve CO insertion to produce species that have ketene-like reactivity. Cyclo addition reactions presented include reaction with imines to form /1-lactams, with alkenes to form cyclobutanones, with aldehydes to form /1-lactones, and with azoarenes to form diazetidinones. Photoinduced benzannulation processes are included. Reactions involving nucleophilic attack to form esters, amino acids, peptides, allenes, acylated arenes, and aza-Cope rearrangement products are detailed. A number of photoinduced reactions of carbenes do not involve CO insertion. These include reactions with sulfur ylides and sulfilimines, cyclopropanation, 1,3-dipolar cycloadditions, and acyl migrations. 

Dalton H, BT Golding, BW Waters, R Higgins, JA Taylor (1981) Oxidation of cyclopropane, methylcyclopro-pane, and arenes with the mono-oxygenase systems from Methylococcus capsulatus. J Chem Soc Chem Commun 482-483. 

H. Dalton, B. T. Golding, B. W. Waters, R. Higgins, J. A. Taylor (1995) Oxidations of cyclopropane, methylcyclopropane, and arenes with the mono-oxygenase system from Methylococcus capsulatus. J. Chem. Soc. Chem. Commun., 1981 482-483... 

Ito and Katsuki (55) examined the use of chiral bipyridine (bpy) compounds as ligands in the asymmetric cyclopropanation of alkenes. Moderate diastereoselectivities and excellent enantioselectivities were observed in the cyclopropanation of vinyl arenes, Eq. 38. This catalyst system afforded very high ee values of the cis isomer. 

A wide range of olefins can be cyclopropanated with acceptor-substituted carbene complexes. These include acyclic or cyclic alkenes, styrenes [1015], 1,3-dienes [1002], vinyl iodides [1347,1348], arenes [1349], fullerenes [1350], heteroare-nes, enol ethers or esters [1351-1354], ketene acetals, and A-alkoxycarbonyl-[1355,1356] or A-silyl enamines [1357], Electron-rich alkenes are usually cyclopropanated faster than electron-poor alkenes [626,1015],... 

Even condensed structures are awkward for cyclic molecules, and a streamlined way of drawing structures is often used in which cycloalkanes are represented by polygons. A triangle represents cyclopropane, a square represents cyclobutane, and so on. Carbon and hydrogen atoms aren t shown explicitly in these structures. A carbon atom is simply understood to be at every junction of lines, and the proper number of hydrogen atoms needed to give each carbon four bonds is supplied mentally. Methylcyclohexane, for instance, looks like this ... 

This reactivity proved to be a general process, providing the unique products in moderate yields following cyclopropanation and immediate treatment with silver tetrafluoroborate. These structures revealed that a cascade sequence was proceeding stereoselectively in every case to furnish a single product as the result of conrotatory 4jt electrocyclization, electrophilic aromatic substitution at the least hindered position on the arene moiety (para to the MeO) in favor of six-membered ring formation, and desilylation with protonation from the exo face of the bicyclic product. Dehydrochlorination to form a second cationic intermediate did not occur in this case, due to structural restrictions imposed by the bridged architecture of 81. 

As (—)-pulegone is not readily available, subsequent work addressed the natural enantiomer by different methods [12], but all completed their synthesis via Snider s enone (17). Asaoka utilised a TMS group as temporary directing volume (Scheme 5) [12a]. Cossy applied a photore-ductive cyclopropane ring opening, which was obtained by a diastereoselective Simmons-Smith reaction [12b]. Schmalz finally used a planar-chiral arene complex to synthesise enone 17 with interesting CrfCO), chemistry [12c]. 

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