Acetates cyclopropanes

The comparison between the cycloaddition behavior of simple diazoketones and of ethyl diazopyruvate 56 towards the same olefin underlines the crucial influence of the ethoxycarbonyl group attached to the carbonyl function. This becomes once again evident when COOEt is replaced by an acetal function, such as in l-diazo-3,3-di-methoxy-2-butanone 86 with enol ethers and acetates, cyclopropanes rather than dihydrofurans are now obtained 113). ... 

The majority of preparative methods which have been used for obtaining cyclopropane derivatives involve carbene addition to an olefmic bond, if acetylenes are used in the reaction, cyclopropenes are obtained. Heteroatom-substituted or vinyl cydopropanes come from alkenyl bromides or enol acetates (A. de Meijere, 1979 E. J. Corey, 1975 B E. Wenkert, 1970 A). The carbenes needed for cyclopropane syntheses can be obtained in situ by a-elimination of hydrogen halides with strong bases (R. Kdstcr, 1971 E.J. Corey, 1975 B), by copper catalyzed decomposition of diazo compounds (E. Wenkert, 1970 A S.D. Burke, 1979 N.J. Turro, 1966), or by reductive elimination of iodine from gem-diiodides (J. Nishimura, 1969 D. Wen-disch, 1971 J.M. Denis, 1972 H.E. Simmons, 1973 C. Girard, 1974),... 

Cyclopropane rings are opened hydrogenolytically, e.g., over platinum on platinum dioxide (Adam s catalyst) in acetic acid at 2 - 4 bars hydrogen pressure. The bond, which is best accessible to the catalyst and most activated by conjugated substituents, is cleaved selectively (W.J. Irwin, 1968 R.L. Augustine, 1976). Synthetically this reaction is useful as a means to hydromethylate C—C double bonds via carbenoid addition (see p. 74f. Z. Majerski, 1968 C.W. Woodworth, 1968). 

Allylic acetates react with ketene silyl acetals. In this reaction, in addition to the allylated ester 468, the cyclopropane derivative 469. which is formed by the use of bidentate ligands, is obtained[303]. Formation of a cyclopropane derivative 471 has been observed by the stoichiometric reaction of the 7r-allylpal-... 

The key step in this sequence, achieved by exposure of 46 lo a mixture of sulfuric acid and acetic anhydride, involves opening of the cyclopropane ring by migration of a sigma bond from the quaternary center to one terminus of the former cyclo-l>ropane. This complex rearrangement, rather reminiscent of the i enone-phenol reaction, serves to both build the proper carbon. keleton and to provide ring C in the proper oxidation state. 

In the reaction with epoxides, y-hydroxysulfones are obtained278-280. For example, Kondo and coworkers279 synthesized various (5-lactols 226 by treating sulfone acetals 225 with terminal epoxides as shown below. Dilithiated phenylsulfonylmethylene reacted with haloepoxide and afforded 3-(phenylsulfonyl)cycloalkanols281. Treatment of y, 5-epoxysulfones 227 and 229 with n-butyllithium resulted in cyclization to form cyclopropane derivatives 228 and bicyclobutane 230, respectively282. 

Much of the early work into the rhodium(II)-catalysed formation of oxazoles from diazocarbonyl compounds was pioneered by the group of Helquist. They first reported, in 1986, the rhodium(II) acetate catalysed reaction of dimethyl diazomalonate with nitriles.<86TL5559, 93T5445, 960S(74)229> A range of nitriles was screened, including aromatic, alkyl and vinyl derivatives with unsaturated nitriles, cyclopropanation was found to be a competing reaction (Table 3). 

Cyclopropanation from the hydroxyl side of (54) should give (53). Removal of the acetal leaves ketone (55) in which the double bond has been returned to conjugation. The structure remaining is very like ketone (56), the classical product of a Robinson annelation (pT175). Analysls... 

Treatment of aromatic aldehydes such as p-anisaldehyde with Zn-powder and l,2-bis(chlorodimethylsilyl)ethane 45 give Zn-carbene adducts such as 2096 which add readily to olefins such as cyclohexene [22, 26] or styrene [26] to give high yields of cyclopropanes such as 2097 and the oxide 47 [26]. Acetals such as 2098 react analogously with cyclohexene to afford the endo and exo cyclopropanes 2099 and 2100 [22, 27] (Scheme 13.11). 

Cyclopropyl sulfones were shown to be obtained either by cyclization of y-p-tosyloxy sulfones 232 with base or by treatment of phenylsulfonylacetonitrile 233a or ethyl phenyl sulfonyl acetate 233b with 1,2-dibromoethane in the presence of benzyltriethyl-ammonium chloride (BTEA) and alkali in good yields. Chang and Pinnick synthesized various cyclopropane derivatives 234 upon initial treatment of carbanions derived from cyclopropyl phenyl sulfone with either alkylating agents or a carbonyl compound and subsequent desulfonylation, as shown below. 

Aziridination of alkenes can be carried out using N-(p- to I ucncsu I I o n y I i m i n o) phenyliodinane and copper triflate or other copper salts.257 These reactions are mechanistically analogous to metal-catalyzed cyclopropanation. Rhodium acetate also acts as a catalyst.258 Other arenesulfonyliminoiodinanes can be used,259 as can chloroamine T260 and bromoamine T.261 The range of substituted alkenes that react includes acrylate esters.262... 

The threo stereoisomer was the major product obtained by the synthesis in Scheme 13.14. This stereochemistry was established by the conjugate addition in Step A, where a significant (4-6 1) diastereoselectivity was observed. The C(4)-C(7) stereochemical relationship was retained through the remainder of the synthesis. The other special features of this synthesis are in Steps B and C. The mercuric acetate-mediated cyclopropane ring opening was facilitated by the alkoxy substituent.19 The reduction by NaBH4 accomplished both demercuration and reduction of the aldehyde group. 

ETHYLENE GLYCOL ETHYL MERCAPTAN DIMETHYL SULPHIDE ETHYL AMINE DIMETHYL AMIDE MONOETHANOLAMINE ETHYLENEDIAMINE ACRYLONITRILE PROPADIENE METHYL ACETYLENE ACROLEIN ACRYLIC ACID VINYL FORMATE ALLYL CHLORIDE 1 2 3-TRICHLOROPROPANE PROPIONITRILE CYCLOPROPANE PROPYLENE 1 2-DICHLOROPROPANE ACETONE ALLYL ALCOHOL PROPIONALDEHYDE PROPYLENE OXIDE VINYL METHYL ETHER PROPIONIC ACID ETHYL FORMATE METHYL ACETATE PROPYL CHLORIDE ISOPROPYL CHLORIDE PROPANE... 

The search for catalysts which are able to reverse the ratio of cyclopropane diastereomers in favor of the thermodynamically less stable isomer has met with only moderate success to date. Rh(II) pivalate and some ring-substituted Rh(II) benzoates induce cw-selectivity in the production of permethric acid esters 77,98 99 contrary to rhodium(II) acetate, which gives a 1 1 mixture 74,77,98), and some copper catalysts 98) (Scheme 10). 

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