Cyclopropyl lithium

Nakajima has shown that a-cyclopropyl acyl silane (23) results from reaction of 1-trimethylsilyl cyclopropyl lithium with dichloromethyl methyl ether at low temperature in THF solution, in a reaction said to involve a carbene intermediate and a 1,2-silicon shift (Scheme 56)147. 

The H chemical shifts and inter-proton coupling constants of cyclopropyl lithium (244) were determined by three groups This compound, apart from its intrinsic interest. 

Cyclopropyl halides, however, and alkyllithiums react to give good yields of cyclopropyl-lithiums. Retention of configuration is found in cyclopropyl halide-alkyl-Li reactions e.g. ... 

Masamune as an intermediate in his amphotericin synthesis.15 Disconnection to the hydroxyacid 36 was particularly attractive as optically active 36 was available. Cyclopropyl-lithium 35 M=Li is actually easier to make than other -alkyl-lithiums as the three-membered ring stabilises the anion in the o-complex.16 Acylation with 36 needed three molecules of 35 R = Li as two are consumed by the acidic OHs, but the reaction is an efficient acylation at carbon. 

An interesting synthesis of ( )-[2 - C]nicotine using the cyclopropyl-imine synthon (for other applications, see Vol. 2, p. 133 and Vol. 3, p. 211) has been reported. Thus treatment of 3-[ C]-cyanopyridine with cyclopropyl-lithium gave, after hydrolysis, the ketone (29) which, when refluxed in N-methylform-amide, produced (+)-[2 - C]nicotine. 

Vinylcyclopropanols have been prepared by the addition of alkenyl Grignard reagents to a variety of cyclopropanone equivalents. Upon treatment with acid, the vinylcyclopropanols rearrange to o-substituted cyclobutanones. Alternatively, a variety of o-heteroatom-substituted cyclopropyl lithium reagents have been developed. These react with aldehydes and ketones to afford cyclopropylcarbinols which also rearrange to cyclobutanones under acid catalysis.Lastly, vinylcyclopropanols and cyclopropylcarbinols have been prepared by the cyclopropanation of enol silyl ethers and allylic alcohols. 

Methods of Synthesis.—No new methodology has been reported during the past two years other than the adaptation of the sulphonium salt ligand-exchange reaction to sulphonium ylide synthesis. Trost et prepared cyclopropylidenediphenylsulphurane (1) by treatment of a triphenyl-sulphonium salt with cyclopropyl-lithium. The same ylide was prepared... 

An improved procedure for the Diels-Alder reaction between cyclo-octatetraene and dimethyl acetylene dicarboxylate to give dimethyl unti-tricyclo[4,2,2,0 ]deca-3,7,10-triene-7,8-dicarboxylate (85 %) has been described. Diels-Alder reactions of maleic anhydride and mono-substituted (Mr, CHjOAc, Ph, CO2CH3. OMe, cyclopropyl substituents) and di-substituted (Me, Me CHjOAc, CHjOAc —(CH2)4— Me, CH2 O Ac substituents) cyclo-octatetraenes have been described cyclopropyl cyclo-octatetraene was obtained from bromocyclo-octatetraene and cyclopropyl lithium. The Diels-Alder reaction between cyclo-octatetraene and acryloyl chloride which gives a mixture of endo- and exo-adducts (80% total yield), was the first step in a reported synthesis of Nenitzescu s hydrocarbon. ... 

T. Cohen, W. M. Daniewski, and R. B. Weisenfeld, Tetrahedron Letters, 1978, 4665. a-Phenylthio-cyclopropyl-lithiums. 

S. Halazy, J. Lucchetti, and A. Krief, Tetrahedron Letters, 1978, 3971. a-Phenylseleno-cyclopropyl-lithiums. 

Treatment of oc-cyclopropyl ketones with lithium in a mixture of N,N-d2 propylamine and hexamethylphosphortriamide is a recently reported method for deuterium labeling via reductive ring opening. This reaction provides y-labeled ketones in good yield (70-100%) and isotopic purity (85-93%). 

The key cyclization in Step B-2 was followed by a sequence of steps that effected a ring expansion via a carbene addition and cyclopropyl halide solvolysis. The products of Steps E and F are interesting in that the tricyclic structures are largely converted to tetracyclic derivatives by intramolecular aldol reactions. The extraneous bond was broken in Step G. First a diol was formed by NaBH4 reduction and this was converted via the lithium alkoxide to a monomesylate. The resulting (3-hydroxy mesylate is capable of a concerted fragmentation, which occurred on treatment with potassium f-butoxide. 

The addition of lithium to dicyclopropylacetylene (556) catalyzed by biphenyl (3%) in THF at —30 °C provoked a carbon-carbon bond cleavage in one of the cyclopropyl rings giving a delocalized dianion 557, which by reaction with dimethyl sulfate at —78 °C gave the aUtene 558 (Scheme 149). ... 

Another feature of carbenoid-type reactivity is the cyclopropanation (reaction c). Again, this reaction does not only take place in vinylidene but also in alkyl carbenoids . On the other hand, the intramolecular shift of a /3-aryl, cyclopropyl or hydrogen substituent, known as the Fritsch-Buttenberg-Wiechell rearrangement, is a typical reaction of a-lithiated vinyl halides (reaction d) . A particular carbenoid-like reaction occurring in a-halo-a-lithiocyclopropanes is the formation of allenes and simultaneous liberation of the corresponding lithium halide (equation 3). ... 

Chelation is another driving force that provides diastereoselective bromine-lithium exchange reactions to give cyclopropyl carbenoids. Thus, the exo-bromine atom in dibro-mocyclopropane 25 is exchanged exclusively due to the methoxy substituent, which encourages the lithium to occupy the cis orientation (equation 16) ° Several representative examples of cyclopropyl bromo lithium carbenoids obtained by bromine-lithium exchange reactions are given in Table 1. 

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