1-alkoxy-1 - cyclopropane alkene

Non-heteroatom-stabilised Fischer carbene complexes also react with alkenes to give mixtures of olefin metathesis products and cyclopropane derivatives which are frequently the minor reaction products [19]. Furthermore, non-heteroatom-stabilised vinylcarbene complexes, generated in situ by reaction of an alkoxy- or aminocarbene complex with an alkyne, are able to react with different types of alkenes in an intramolecular or intermolecular process to produce bicyclic compounds containing a cyclopropane ring [20]. 

Some remarks concerning the scope of the cobalt chelate catalysts 207 seem appropriate. Terminal double bonds in conjugation with vinyl, aryl and alkoxy-carbonyl groups are cyclopropanated selectively. No such reaction occurs with alkyl-substituted and cyclic olefins, cyclic and sterically hindered acyclic 1,3-dienes, vinyl ethers, allenes and phenylacetylene95). The cyclopropanation of electron-poor alkenes such as acrylonitrile and ethyl acrylate (optical yield in the presence of 207a r 33%) with ethyl diazoacetate deserve notice, as these components usually... 

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... 

Epoxides such as 10 can be prepared in high enantiomeric purity, by, inter alia, kinetic resolution. David Hodgson of Oxford University has demonstrated (J. Am. Chem. Soc. 2004, /26,8664) that on exposure to LTMP, monosubstituted epoxides are smoothly converted into the corresponding alkoxy carbenc or alkoxy carbenoid. When an alkene is available for insertion, the cyclopropane, in this case 11, is formed with high diastereocontrol. This represents a powerful new approach to enantioselective ring construction. It is possible that in the absence of a target alkene, the intermediate alkoxy carbene could divert to intramolecular C-H insertion, which might also proceed with substantial diastereocontrol. 

The reactions of these iron carbene reagents with alkenes to give cyclopropanes are stereospecific. They also exhibit high syn stereoselectivity in many cases. Optically active derivatives have been reported that have chiral ligands on iron or chiral alkoxy groups on the prospective caibene center and which have been resolved with the iron itself as a chiral center. Resulting from this work have been some highly enantioselective cyclopropanations. 

Diastereoselective and enantioselective (see Enantio-selectivity) cyclopropanations of chiral alkenes can be achieved (Scheme 57). Unactivated alkenes usually do not participate in cyclopropanation reactions of Fischer carbenes. However, alkenyl- and heteroaryl-substituted group 6 alkoxy carbene complexes cyclopropanate unactivated alkenes in good yield (Scheme 58). ... 

The transient zirconocene butene complex, 105, has proved to be useful in a number of organic transformations. For example, butene substitution of zirconocene alkene complexes with alkoxy-substituted olefins results in /3-alkoxide elimination to furnish the zirconocene alkoxy compounds (R = Me, 123 R = Bnz, 124) (Scheme 16).50,51 Addition of propargyl alcohols to the zirconocene butene complex, 105, affords homoallylic alcohols. These reactions are of limited utility owing to the lack of stereoselectivity or formation of multiple products. Positioning the alkoxide functional group further down the hydrocarbyl chain allows synthesis of cyclopropanes, though mixtures of the carbocycle and alkene products are obtained in some cases (Scheme 16).52... 

Bis(organooxy)diazirines are available by exchange of chlorine in 3-alkoxy-3-chloro-3//-diazirines for the alkoxy group. The diazirines thus formed decompose under mild conditions, at room temperature, to generate the bis(organooxy)carbenes which undergo addition to electrophilic alkenes to give cyclopropanes... 

Cobalt is another metal which has been successfully used in asymmetric cyclopropanation. A chirally modified catalytic system for selective cyclopropanation of phenyl-, vinyl- or alkoxy-carbonyl-conjugated terminal double bonds with diazoacetates is formed from cobalt(ll) chloride and (+)-a-camphorquinonc dioxime27,69 71 and similar systems 09. Best optical yields are achieved with styrene and the bulky 2,2-dimethylpropvl diazoacetate which gives 2,2-dimethylpropyl /ra .v-2-phenyl-l-cyclopropanecarboxylate in 88% ee and the as-isomer in 81%ee7n. No cyclopropanation occurs with alkyl-substituted or cyclic alkenes, cyclic or sterically hindered acyclic 1.3-dienes, vinyl ethers and phenylethyne. 

Extension to the use of acrylates afforded the desired olefination products as a mixture of the desired alkene and intra-molecnlar alkoxy-Michael addition products in high ee. Analogous methodology has been extended to the asymmetric intra-molecular lactonization of diphenylacetic acids toward benzofuranones as well as the enantioselective iodination of diaryl pyridines and methylamines. Asymmetric C—H activation of cyclopropanes has also been reported. ... 

Even [3-1-2] cycloadditions occur when cyclopropyl ketones are treated with (1) under photolytic or Lewis acid conditions to produce cyclopentane systems. Cyclopropanations of (1) are well known, in all cases adding to the more electron-rich sUy-loxy alkene. The vinylcyclopropanol silyl ethers can be converted into a number of different products, e.g. cyclopentanones, 2-methylcyclobutanones, vinyl ketones, and -alkoxy ketones (eq 10). One clever use of (1) in synthesis is the tandem [2 + 21-Cope process which converts (34) into (35) (eq 11). ... 

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