Cyclopropylcarbinyl compounds

CychpropykarHnyl comptmnds. Electrophilic reagents (CI2. SO3, RSCl, HgClj) add to. 3-butenyltri-ii-butyllin to give cyclopropylcarbinyl compounds in 72-86% yield. 

CYCLOPROPYL AZIDES Mercuric azide. CYCLOPROPYLCARBINYL COMPOUNDS 3-Butenyitri-n-butyltin. CYCLOPROPYL KETONES Potassium t-buloxide. Sodium ethoxide. Sulfuric add. 1,3-DEHYDROADAMANTANES n-Butyi-lithium. 

Cyclopropanes, 101, 267 Cyclopropanone ketals, 315-316 Cyclopropene, 113 Cyclopropenone, 519 Cyclopropenones, 27, 399 Cyclopropylacetylene, 401 Cyclopropyl azides, 323 Cyclopropylcarbinyl compounds, 53 Cyclopropyldiphenylsulfonium fluoroborate, 211,213-214... 

Cyclopropylcarbinylcompounds.1 Electrophilic reagents (Cl2, S03, RSC1, HgCl2) add to 3-butenyltri-n-butyltin to give cyclopropylcarbinyl compounds in 72-86 % yield. 

Vasse J-L, Szymoniak J (2004) Access to functionalized cyclopropylcarbinyl compounds from homoallylic ethers via zirconocene intermediates. Tetrahedron Lett 45 6449-6451... 

Cu(II) EPR signal in nitriles as solvent as well as by polarographic measurements 144>. Similarly, the EPR signal disappeared when Cu(OTf)2 was used for catalytic cyclo-propanation of olefins with diazoesters 64). In these cases, no evidence for radical-chain reactions has been reported, however. The Cu(acac)2- or Cu(hfacac)2-eatalyzed decomposition of N2CHCOOEt, N2C(COOEt)2, MeCOC(N2)COOEt and N2CHCOCOOEt in the presence of cyclopropyl-substituted ethylenes did not furnish any products derived from a cyclopropylcarbinyl - butenyl rearrangement128. These results rule out the possible participation of electron-transfer processes and radical intermediates which would arise from interaction between the olefin and a radical species derived from the diazocarbonyl compound. 

Compounds 102 and 103 are products of cyclopropylcarbinyl rearrangements under the reaction conditions, and compound 104 is the product of an ene reaction . Relative reactivities of 96 with furan (7), 2,3-dimethylbutadiene (35), 1,3-cyclohexadiene (26) and cyclopen tadiene (6) were estimated to be 1 2.5 2.5 50, respectively [27]. 

X-ray crystallographic studies of the cyclopropylcarbinyl cations have so far been mainly confined to the hydroxycyclopropylcarbinyl cations, generated from the corresponding carbonyl compounds. Typically, the corresponding hexafluoroantimonate salts were prepared by treating the carbonyl compounds with HF-SbF5, and single-crystal X-ray diffractions were carried out. Childs and coworkers have obtained several X-ray structures on such cations as 135-14017. 

A set of rapidly equilibrating carbenium ions might account for the rearrangements and the label scrambling but this cannot be the correct explanation, for cyclopropylcarbinyl, cyclobutyl, and allylcarbinyl systems all solvolyze much more rapidly than would be expected from model compounds. Thus, for example, the rate of solvolysis of cyclopropylcarbinyl tosylate is 10 times that of the solvent-assisted solvolysis of isobutyl tosylate.77 Cyclobutyl tosylate solvolyzes 11 times... 

That maximum acceleration occurs when the vacant p orbital is parallel to the plane of the cyclopropyl ring can be seen from the solvolysis of spiro[cyclo-propane-l,2 -adamantyl] chloride (71). The carbocation formed by departure of Cl is unable to adopt the geometry of the bisected cyclopropylcarbinyl cation, but can orient its empty p orbital properly to form the bicyclobutonium ion. This compound solvolyzes 103 times more slowly than 1-adamantyl chloride.82 On the other hand, 72 solvolyzes 10s times faster than 73. The cation from 72 does have its p orbital parallel to the plane of the ring as in the bisected cyclopropylcarbinyl cation.83... 

A wide range of alkenes may be used as substrates. The reaction is most commonly performed with alkenes of normal electronic nature, but electron deficient alkenes, such as a, 3-unsaturated carbonyl compounds, and very electron rich alkenes, such as enol ethers and enamines, have also been used successfully. Not surprisingly, the cyclopropylcarbinyl ethers and amines that are formed in the latter reactions (see Table S) are subject to facile rearrangements. 

The Barton-McCombie reaction of bicyclo[3.1.0]-, [4.1.0]-, and [5.1.0]-imidazoylthio-carbonates (264) induces the formation of cyclopropylcarbinyl radicals, and subsequent (3-cleavage, to generate one-carbon ring-expanded 6-, 7-, and 8-membered compounds (265) in good yields [271]. The driving force of these reactions is the reduction of ring strain (eq. 3.106). 

Eq. 3.119 shows the preparation of a spiro compound (289) through 5-exo-trig ring closure to form a cyclopropylcarbinyl radical, followed by (3-cleavage, and subsequent 5-exo-trig ring closure to imino-carbon [299-301]. 

Later Julia and coworkers developed another important mode of ring breaking addition of Grignard compounds or reduction converts the ester 22 to the corresponding alcohols which are startingpoints for a cyclopropylcarbinyl/homoallyl cation rearrangement. After acid treatment p/y-unsaturated carbonyl compounds (e.g. 23) can be isolated, which sometimes isomerize to the oc,(3-unsaturated systems 10). 

The reduction of methyl 2-siloxycyclopropanecarboxylates can also be started at the ester function when lithium aluminum hydride in ether is the reagent. The resulting alcohols undergo the wellknown cyclopropylcarbinyl/homoallyl rearrangement upon treatment with acid to provide P/y-unsaturated carbonyl compounds 117. These are synthesized isomerically pure and in good yields in a number of cases, if the two-phase-system 2N hydrochloric acid/pentane is employed 78). Otherwise the very easy isomerization to the conjugated a,p-unsaturated compounds 118 occurs to some extend, which can intentionally be completed by base catalysis. 

Further evidence for singlet 1,4-diradical intermediates has been obtained in the case of photocycloaddition of cyclopropanecarbaldehyde with ( )-penta-1,3-diene, in which the formation of the cyclopropyl-oxetane (PS) dominated. This is in contrast to the case of aromatic carbonyl compounds and cyclopropylethylene in which the formation of considerable amounts of ring-opened products and ox-epins, formed by cyclopropylcarbinyl-allylcarbinyl rearrangement, implicates the intermediacy of a triplet 1,4-diradical. ... 

The cyclopropylimine ynoline rearrangement (equation 68) has been exploited by Stevens in alkaloid syntheses. - Wenkert s cyclopropylcarbinyl rearrangement (equation 69) served extremely well in the design of 1,4-dicarbonyl synthons or 3,-y-unsaturated carbonyl compounds which then were expressed in numerous syntheses of terpenoid and alkaloid natural products. Donor-acceptor concepts continue to be express in the applicability of these rearrangements to organic synthesis. 

The stabdities of protonated cyclopropylcarbinyl ketones are a long-standing puzzle. Richie provided evidence that the bisected cyclopropylcarbinyl carbenium ion (66a) was the more stable conformation, rather than the perpendicular geometry (66b). Of the protonated, rigid ketones, (67), (68), and (69), spiro compoimd (67) is most stable, but the bicyclo compound (68) proved more stable than the nortricyclic system (69), although the latter has a bisected geometry, while (68) is imable to achieve this. The anomaly appears to have been resolved by semiempirical calculations of heats of formation of the ketones and ions, and an analysis of the effects of syn- and... 

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