Esters cyclopropyl

The complex [Fe(D4-TmAP)Cl] with Halterman s porphyrin ligand can effect asymmetric alkene cyclopropanation with diazoacetate in high product yield and high stereoselectivity [57]. The reaction occurs smoothly at room temperature without the need for addition of CoCp2, affording the cyclopropyl esters... 

Note that we predict ring opening of the cyclopropyl cation to require activation this at first sight seems to be at variance with evidence that rearrangement occurs as a concerted process in the solvolysis of cyclopropyl esters and indeed acts as a driving force 44). Moreover the evidence shows very clearly that this is so only for one of the possible disrotatory processes, i.e. that indicated in 25 ... 

Analogous ring opening of cyclopropyl esters with Sml2 were also reported in 1994 by Imamoto, Hatajima and Yoshizawa (equation 13).58b... 

Intermolecular cyclopropanation reactions with ethyl diazoacetate have been employed for the construction of the cyclopropane-containing amino acid 7 (equation 25) Thus, rhodium(II) acetate catalysed decomposition of ethyl diazoacetate in the presence of d-cbz-vinylglycine methyl ester 5 afforded cyclopropyl ester 6 in 85% yield. Removal of the protecting group completed the synthesis of 7. Another example illustrating intermolecular cyclopropanation can be found in Piers and Moss synthesis of ( )-quadrone 8" (equation 26). Intermolecular cyclopropanation of enamide or vinyl ether functions using ethyl diazoacetate has also been used in the synthesis of eburnamonine 9", pentalenolactone E ester 10" and ( )-dicranenone A11" (equations 27-29). 

Alumina-catalyzed conversion of either isomer of (193) to dihydrofuran (194) was reported as an alternative to acid-catalyzed conditions (equation 57). A methodology of a-methylene lactone synthesis relies on the solvolysis of cyclopropyl esters of type (195) to give u-methylote lactone (196) with Li2C03 in dioxane (equation 58). The formation of fte undesired diene (197) was diminished by the use OfAgC104.235... 

The low tendency of cyclopropyl esters to form the ester enolate is also documented by the following examples Boche and Martens have reported that methyl cis-bicyclo[6.1.0]nona-2,4,6-triene-flnti-9-carboxylate (227) loses a proton at C(l) when treated with LDA to give, probably via the cyclopropyl anion 228", the allyl anion 229". Russell and coworkers have shown that ethyl 2-methyl-2-nitrocyclopropanecarboxylate (230) gives the 2-methylenecyclopropanecarboxylate (231) when treated with sodium hydride. 

A successful trapping reaction of a cyclopropyl ester enolate with trimethylsilyl chloride (TMSC) was first performed by Ainsworth and coworkers . In the reaction of 232 with lithium diisopropyl amide at — 78°C, followed by addition of TMSC, the ketene acetal 233 was formed in 10% yield as well as the silylated cyclopropane 234 (40%). Ketene acetals other than 233 are formed in yields > 90 %. 

That it is indeed the planarity of cyclopropyl (ester) enolates that causes extra strain and thus instability and high reactivity of such anions, as well as low acidity of the corresponding C(0)-substituted cyclopropanes, has been firmly established . It was shown that treatment of ( —)-(R)-l-benzoyl-2,2-diphenylcyclopropane... 

Finally, there has also been research into the ozonolysis of allenes. Thus sterically hindered allenes react by transfer of one oxygen atom, forming a mixture of reaction products Recently, the ozonolysis of a cyclopropylallene has been shown to yield a diastereomeric mixture of cyclopropyl esters. ... 

So far, while there is a relative abundance of synthetically useful cyclopropana-tion catalysts, all of them provide a mixture of diastereomers with the anti product predominating. Thus, a catalyst able to provide optically active syn cyclopropyl esters would constitute a useful complement to existing methodology. Rhodium complexes of bulky porphyrins ( chiral fortress porphyrins) have been developed for this purpose [27]. The porphyrin ligands bear chiralbinaphthyl groups appended directly to the meso positions. Their rhodium(III) complexes provide predominantly the syn cyclopropane with diazoesters, with very good stereoselectivity in some cases. However, the enantioselectivities observed are modest. 

A large number of cyclopropanes containing a bond from oxygen to a cyclopropyl carbon atom have been synthesized from other cyclopropanes by substitution of a variety of substituents. The reagents utilized and the reaction conditions employed to achieve the transformations depend on the type of compound being prepared. The compounds can be divided into four groups cyclopropanols, cyclopropyl ethers, cyclopropyl esters, and oxaspiropentanes. 

Cyclopropyl esters can be aflforded by substitution from a variety of different substrates. Almost all esters prepared are acetates. Even a hydrogen atom can be directly replaced by an acetate group. Thus, when tetracyclo[3.3.1.0. 0 - ]nonane (triaxane) was treated with lead(IV) acetate, 2-acetoxytetracyclo[3.3.1.0 . 0 ]nonane (1) was obtained in 72% yield together with exo-4-acetoxy-ant(-8-acetoxytricyclo[4.2.1.0 ]nonane (2, 17%). ... 

Reductive carbonylation of 1,1-dibromocyclopropanes with tetracarbonylnickel in dimethyl-formamide in the presence of a nucleophile is a powerful method for direct introduction of carboxylic acid functions to cyclopropanes. Nucleophiles, such as alcohols, amines, and silylamines, are particularly reactive and give cyclopropyl esters and amides, respectively, in reasonable to good yields, e.g. formation of 5 and... 

A number of cyclopropyl esters and have been transformed to cyclo-... 

Cyclopropanols can be converted to various cyclopropyloxy derivatives (esters, e.g. acetates, ethers, e.g. methyl and ethyl ethers, and acetals, e.g. tetrahydropyran-2-yloxy derivatives) under the appropriate reaction conditions. In most cases the synthesis of cyclopropyl esters by the reaction between a cyclopropanol and an acid chloride (e.g. formation of 1 ) or acetic anhydride (e.g. formation of 2 ) have been reported. The yields were particularly good (84-95%) when acetic anhydride was used, although a drawback of the reaction can be byproduct formation. When a reactive moiety is attached to the cyclopropane ring in addition to the hydroxy group, other reactions can also occur m-l-(aminomethyl)-2,2-dimethyl-3-(2-methylprop-l-enyl)cyclopropanol (3) reacted with phosgene in benzene to give the corresponding carbamate l,l-dimethyl-2-(2-methylprop-l-enyl)-4-oxa-6-azaspiro[2.4]heptan-5-one (4) in 31% yield. ... 

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