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Alkenes cyclopropanations

In addition to catalytically active transition metal complexes, several stable, electrophilic carbene complexes have been prepared, which can be used to cyclopropanate alkenes (Figure 3.32). These complexes have to be used in stoichiometric quantities to achieve complete conversion of the substrate. Not surprisingly, this type of carbene complex has not attained such broad acceptance by organic chemists as have catalytic cyclopropanations. However, for certain applications the use of stoichiometric amounts of a transition metal carbene complex offers practical advantages such as mild reaction conditions or safer handling. [Pg.105]

Because electrophilic carbene complexes can cyclopropanate alkenes under mild reaction conditions (Table 3.1) [438,618-620], these complexes can serve as stoichiometric reagents for the cyclopropanation of organic compounds. Thoroughly investigated carbene complexes for this purpose are neutral complexes of the type (C0)5M=CR2 (M Cr, Mo, W) and cationic iron(IV) carbene complexes. The mechanism of cyclopropanation by electrophilic carbene complexes has been discussed in Section 1.3. [Pg.106]

Mechanistically, the reaction initially proceeds through the formation of the zinc aUcox-ide, which then complexes a second equivalent of the reagent, and then undergoes a pseudo-intramolecular cyclopropanation (equation 48). It is therefore implicit that 2 equivalents of zinc are needed in these reactions, since the ethylzinc alkoxide does not form the corresponding iodomethylzinc alkoxide in the presence of iodomethane, and the latter does not cyclopropanate alkenes in the absence of a Lewis acid. [Pg.256]

In contrast to the carbene and carbenoid chemistry of simple diazoacetic esters, that of a-silyl-a-diazoacetic esters has not yet been developed systematically [1]. Irradiation of ethyl diazo(trimethylsilyl)acetate in an alcohol affords products derived from 0-H insertion of the carbene intermediate, Wolff rearrangement, and carbene- silene rearrangement [2]. In contrast, photolysis of ethyl diazo(pentamethyldisilanyl)acetate in an inert solvent yields exclusively a ketene derived from a carbene->silene->ketene rearrangement [3], Photochemically generated ethoxycarbonyltrimethyl-silylcarbene cyclopropanates alkenes and undergoes insertion into aliphatic C-H bonds [4]. Copper-catalyzed and photochemically induced cyclopropenation of an alkyne with methyl diazo(trimethylsilyl)acetate has also been reported [5]. [Pg.149]

Cyclopropanation reactions of nonheteroatom-stabilized carbenes have also been developed. The most versatile are the cationic iron carbenes that cyclopropanate alkenes with high stereospecificity under very mild reaction conditions. The cyclopropanation reagents are available from a number of iron complexes, for example, (9-alkylation of cyclopentadienyl dicarbonyliron alkyl or acyl complexes using Meerwein salts affords cationic Fischer carbenes. Cationic iron carbene intermediates can also be prepared by reaction of CpFe(CO)2 with aldehydes followed by treatment with TMS-chloride. Chiral intermolecular cyclopropanation using a chiral iron carbene having a complexed chromium tricarbonyl unit is observed (Scheme 61). [Pg.3230]

A number of heteroatom-substituted dilakylaluminum compounds (R2AICH2-X) can undergo apparent a-, aP-, or ay-eliminations. The apparent a-elimination, when halomethylaluminum compounds cyclopropanate alkenes, is actually a combination of carboalumination and elimination [Eq. (6.87)]. Such eliminations involve hypercarbon intermediates or transition states. [Pg.353]

A cycloctenone synthesis is based on the [5+2+l]cycloaddition in which alkenyl-cyclopropane, alkene, and CO are the participants. The reaction is carried out under CO and N2 (0.2 and 0.8 atm., respectively). Its synthetic potential is illustrated in an approach to hirsutene. ... [Pg.62]


See other pages where Alkenes cyclopropanations is mentioned: [Pg.75]    [Pg.106]    [Pg.2028]    [Pg.2163]    [Pg.2163]    [Pg.2354]    [Pg.2402]    [Pg.2429]    [Pg.2536]    [Pg.2582]    [Pg.118]    [Pg.3229]    [Pg.333]    [Pg.2028]    [Pg.2163]    [Pg.2354]    [Pg.2402]    [Pg.2429]    [Pg.2536]    [Pg.1199]    [Pg.1290]    [Pg.2391]    [Pg.2402]    [Pg.2529]    [Pg.3228]    [Pg.1200]   


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1 - cyclopropane- alkene carboxylate ester

1 -halo-1 - cyclopropane alkene

1-alkoxy-1 - cyclopropane alkene

2- alkene-1,6-dione cyclopropane

3-silyloxy-1 -alkene cyclopropane

Addition of Carbenes to Alkenes Cyclopropane Synthesis

Alkene complexes cyclopropanation

Alkene cyclopropanes from

Alkene derivatives cyclopropane derivative formation

Alkenes Simmons-Smith cyclopropanation

Alkenes conversion into cyclopropane

Alkenes cyclopropanation

Alkenes cyclopropanation

Alkenes cyclopropanation using zinc carbenoids

Alkenes cyclopropanations, diazo methane

Alkenes cyclopropanations, dicarbonyl

Alkenes with cyclopropane ring

Alkenes, -cycloaddition with cyclopropanes

Asymmetric Alkene Cyclopropanation Reactions

Chiral alkenes, stereoselective cyclopropanation

Chiral auxiliaries stereoselective alkene cyclopropanation

Copper compounds alkene cyclopropanation

Cyclopropanation, Epoxidation, and Aziridination of Alkenes (Cu, Rh, Mn, Ti)

Cyclopropanation, of alkenes

Cyclopropane 3-alken

Cyclopropane 3-alken

Cyclopropane alkene

Cyclopropane alkene

Cyclopropane, alkene-like reactions

Cyclopropane, alkene-like reactions rearrangement

Cyclopropane, allylidenesynthesis via Peterson alkenation

Cyclopropane, angle strain from alkenes

Cyclopropane-1,1-dicarbonitrile alkene

Cyclopropanes alkene carbopalladation

Cyclopropanes alkenes by carbene addition

Cyclopropanes and alkenes

Cyclopropanes from carbene reaction with alken

Cyclopropanes from carbenes + alkenes

Cyclopropanes, from carbene additions alkenes

Enantioselective cyclopropanation of alkenes

Laser flash photolysis alkene cyclopropanation

Mechanism, cyclopropane ring alkenes

Peterson alkenations 1 - cyclopropane

Preparation cyclopropanes from alkenes, zinc

Rhodium compounds alkene cyclopropanation

Stereoselectivity alkene cyclopropanation

Unfunctionalized alkenes, stereoselective cyclopropanation

Zinc carbenoids alkene cyclopropanation

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