Cyclopropanes Grignard reaction

The unusual cyclopropane 551 was isolated [probably as the (5)-isomer] from Pistacia vera, together with the hydrated analog 552 551 was synthesized by Grignard reaction of cyclopropylmagnesium bromide with 4-methyl-3-cyclohexenone, and the diol 552 by lithium aluminum reduction of the epoxide of 551. ... 

Figures 7.23 and 7.24 give product yields for Grignard reactions of eyelopropyl bromide (CpBr) in DLF. [98. In these experiments, yields of RMgBr were determined by litraiion, checked in several cases by proionalion and determination (volumetric) of the cyclopropane evolved. Other yields were determined by GC, using authentic samples and GC-MS lo assign GC peaks.

For Grignard reactions of at least some aryl halides, including haloben/.enes. pathway R appears to be minor. Apparently, a dianionic pathway X dominates, liven though dianionic pathways have not been detected in electrochemical reductions of aryl and other halides, there is clear evidence tor them in certain chemical reductions, including those of I-halo-1-main 1-2.2-diphenyl cyclopropanes. Reactions of vmyl halides appear to resemble those of cyclopropyl and aryl halides. 

Conjugate additions. Y"Chloro-a,P-unsaturated sulfoxides give cyclopropane derivatives on Grignard reactions. Apparently, intramolecular displacement of the Y Chloro substituent in the a-sulfmyl anion intermediates is highly favorable. 

Organic halides play a fundamental role in organic chemistry. These compounds are important precursors for carbocations, carbanions, radicals, and carbenes and thus serve as an important platform for organic functional group transformations. Many classical reactions involve the reactions of organic halides. Examples of these reactions include the nucleophilic substitution reactions, elimination reactions, Grignard-type reactions, various transition-metal catalyzed coupling reactions, carbene-related cyclopropanations reactions, and radical cyclization reactions. All these reactions can be carried out in aqueous media. 

This reaction is extended to the intramolecular ring closure of the intermediate radical 224 with olefinic or trimethylsilylacetylenic side chains [121]. Cu(BF4)2 is also effective as an oxidant (Scheme 89) [122]. Conjugate addition of Grignard reagents to 2-eyclopenten-l-one followed by cyclopropanation of the resulting silyl enol ethers gives the substituted cyclopropyl silyl ethers, which are oxidized to 4-substituted-2-cyclohexen-l-ones according to the above-mentioned method [123]. (Scheme 88 and 89)... 

Grignard gives the tertiary alcohol after hydrolysis. Reaction of the alcohol with hydrochloric acid proceeds with rearrangement and opening of the strained cyclopropane to give a chloride. Sn2 displacement of the chloride with dimethylamine forms amitriptyline. Alternatively, dibenzosuberone can be reacted with dimethylaminopropyl Grignard to form an alcohol, which upon dehydration forms amitriptyline. 

Hydroxymethylated cyclopropenes, which can be readily prepared by Rh-catalyzed reaction of diazoesters and alkynes, are good snbstrates for nncatalyzed and Cu-catalyzed carbomagnesiation. For example, a range of substitnted cyclopropanes 82 can be synthesized in a regio- and stereoselective fashion by the Cu-catalyzed addition of Grignard reagents to (3-hydroxymethyl)cyclopropenes 81 (Scheme 57) . 

An asymmetric cyclopropane synthesis has been achieved by the addition-cyclization reaction of a chiral a,/ -unsaturated sulfoxide with a Grignard reagent (equation 32)49. 

Alternatively, the reaction of cyclopropylethynylmagnesium bromide with cyclo-propanone hemiacetal gives l-(cyclopropylethynyl)cyclopropanol (equation 152)232. The reaction of cyclopropanone acetal with other alkynyl Grignard reagents serves as a general route to alkynylcyclopropanols. Similarly, alkynyllithium derivatives of vitamin D were coupled with cyclopropane carbonyl isoxazolidine to give the corresponding alkynyl-cyclopropyl ketones (equation 153). 

The reaction of CHBr3 and CHCI3 with magnesium under Grignard conditions was shown to form cyclopropanes in the presence of alkenes.31 Treatment of 1,1,1,3-tetrahalopropanes (21 X = Cl, Br, F Y, Z = Cl or Br) with KOBif or alkali metal hydroxides under phase transfer conditions in the presence of excess alkene gave rise to cyclopropanes via a postulated alk-l-ynylhalocarbene (22).32... 

---