Intramolecular cyclopropanations, benzene

Reduction of unsaturated aromatic aldehydes to unsaturated hydrocarbons poses a serious problem, especially if the double bond is conjugated with the benzene ring or the carbonyl or both. In Clemmensen reduction the a,)8-unsaturated double bond is usually reduced [160], and in Wolff-Kizhner reduction a cyclopropane derivative may be formed as a result of decomposition of pyrazolines formed by intramolecular addition of the intermediate hydrazones across the double bonds [280]. The only way of converting unsaturated aromatic aldehydes to unsaturated hydrocarbons is the reaction of... 

Maas and co-workers have elaborated the approach to l-oxa-2-silacyclo-pentene derivatives based on cyclization of a siloxyalkylidenecarbene. Thus, as a result of intramolecular aliphatic C — H insertion of the carbene derived from diazo ketone 576, l-oxa-2-sila-4-cyclopentenes 577 were obtained in high yields. Here, the insertion may occur in primary, secondary, and tertiary C—H bonds (87CB635 94JOM115). When no C—H bond is adjacent to the Si atom, as in substrate 578, the cyclopropanation of a benzene ring with concomitant ring expansion may result in oxasilacyclopentene 579 (86CC1782). Photolysis or catalytic decomposition of bissilanes 580 furnishes fused bicyclic heterocycles 581 in moderate yields (90JOM229). 

With p-nitroperbenzoic acid, (105b) led to (116) which on treatment with triphenylphosphine in benzene afforded (117) as minor product and (118). With sodium methoxide, (118) afforded (119), a cyclopropane derivative in the nonnatural 9a-10a series, by an intramolecular 5N2-type reaction (Scheme 13). 

Cyclopropane derivatives, containing an acetate or an oxo function next to a C-C double bond, are photochemically reactive, undergoing intramolecular rearrangements upon irradiation, in a seemingly suprafacial fashion.Thus, photolysis of exo-4-acetyl-3,7,7-trimethylbicyclo[4.1.0]hept-2-ene in benzene gave exo-2-acetyl-3,7,7-trimethylbicy-elo[4.1.0]hept-3-ene.2 ... 

Reaction with benzene follows a similar pathway, yielding a bicyclo[3.2.2]nonatriene structure. Vinylcarbenoids also react with pyrroles to give tropanes via a cyclopropanation-Cope rearrangement route. The direct addition of carbenes to acetylenes does not give satisfactory yields of cyclopropanes, but the rhodium carboxylate catalysed reaction of diazo compounds with acetylenes is a useful source of cyclopro-panes. Carbenoids can also attack a carbonyl oxygen atom, giving rise to a zwitterion (249). An excellent review of intramolecular carbenoid reactions has appeared. ... 

Friedel-Crafts alkylations of chlorobenzene, chloropropylbenzenes, and p-xylene by cyclopropane have been examined, employing sulphuric acid and aluminium trichloride as catalysts. The alkylation of benzene, toluene, and anisole by 1-bromo-1-fluorocyclopropane results in indanes, indenes, and alkenylbenzenes. Intramolecular acylation of (183) affords products of attack at C-1 and C-2 of the cyclo-... 

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