3.3- Disubstituted cyclopropene

Cycloalkene Derivatives Cyclopropenes readily interact with nitrile oxides. Reactions of a broad series of 3,3-disubstituted cyclopropenes with 4-substituted benzonitrile, methoxycarbonyl- and cyanoformonitrile oxides (229) as well as with di(isopropoxy)phosphorylformonitrile oxide (230) give 2-oxa-3-azabicyclo[3.1.0]hexene derivatives 62. Stereoselectivity of the cycloaddition is governed by both steric and polar factors. In particular, steric factors are supposed to prevail for 3-methyl-3-phenylcyclopropene affording 62 [R1 =... 

Addition of distannane to alkenes has been achieved only with strained cyclopropenes (Equation (60)).158 3,3-Disubstituted cyclopropenes undergo highly face-selective distannation in the presence of the palladium-isocyanide complex to afford m-adducts. 

The intermediacy of >/2-cyclopropene complexes of nickel has been proposed in catalyzed 2+1 reactions of free cyclopropene with electron-poor olefins, to give vinylcyclo-propanes. For example, the reaction of fumarate esters with 3,3-disubstituted cyclopropenes in the presence of Ni(COD)2 catalyst gave vinyl-substituted trans-2,3-cyclopropane dicarboxylate esters (equation 235)72 302. However, when maleic esters were used instead, a mixture of both cis and trans vinylcyclopropane diesters is obtained. 

Without question, the most important developments in this field over the past 10 years have been in the area of enantioselective hydroborations. New chiral catalyst systems are typically tested in hydroborations of vinyl arenes, as reactions using HBcat and a cationic rhodium catalyst are well known to give selective formation of the unusual branched isomer. In related studies, enantiopure 2,2-disubstituted cyclopropyl boronates were easily prepared via the catalytic asymmetric hydroboration of 3,3-disubstituted cyclopropenes using a number of chiral neutral rhodium complexes (equation 13). Directing groups, such as esters and alkoxymethyl substituents, were necessary for achieving... 

Disubstituted cyelopropenes. The McMurry coupling reaction is convenient for preparation of 3,3-disubstituted cyclopropenes of type 3 and 4, even, though these products are considerably strained (equation I). 

In most cases, cyclopropene and its derivatives are easily prepared l5>. Especially the 3,3-disubstituted cyclopropenes can be obtained on a multigram scale in a two-step process 24-26) with overall yields as high as 80% (Eq. 1)... 

This method has been extended to other 3,3-disubstituted cyclopropenes 74). The structure of 29 which has primarily been derived from spectroscopic data W), has been confirmed by a three-dimensional X-ray analysis 100). The two sy -oriented dimethyl-cyclopropyl rings impose steric strain on the molecule which faciliates the thermal rearrangement to hexamethyl-trans-tricyclo[4.3.0.07,9]non-3-ene (30)1015 (Eq. 39).. 

The reaction of 3,3-disubstituted cyclopropenes with mono- and 1,2-disubstituted alkenes proceeds only with difficulty and leads to low yields of cyclopropanes. In the case of but-l-ene, an 8% yield, with hex-1-ene and hept-l-ene between 5 and 10% yield, and with cyclooctene about 10% of the cyclopropane product is formed. In these cases, the major product is the formal dimer of the intermediate ethenylcarbene complex, i.e. the corresponding (fj-hexatriene. When copper(I) chloride is used as catalyst rather than the copper halide/phosphane or phosphite system, about half the yield of the [2-f-1] cycloadduct is obtained along with an increased amount of the hexatriene. Mechanistically, these acyclic trienes could also be formed from an (alk-l-enyl)bicyclo[1.1.0]butane intermediate without any carbene being involved. Bicyclo[1.1.0]butanes are low yield (< 20%) byproducts of the thermal dimerization reaction of methyl 3,3-dimethylcyclopropenecarboxylate (1). On the other hand, bicyclo[l. 1. Ojbutanes, such as 3, are known to undergo isomerization to form 1,3-dienes. ... 

Table 2. [2 + 1] Cycloadducts by Reaction of 3,3-Disubstituted Cyclopropenes with 1,1-Disubstituted Alkenes or Cyclopentadienes...

Table 3. Formation of Substituted 2-(Alk-l-enyl)cyclopropanecarboxylates by [2 + 1] Cycloaddition of 3,3-Disubstituted Cyclopropenes and Alkenes with Electron-Withdrawing Substituents in the Presence of Bis( -cycloocta-l,5-diene)nickel(0)...

Remarkably, with 3,3-dimethoxycyclopropene, the stereochemical outcome of the [2 4-1] cycloaddition reaction with dialkyl fumarate and maleate is different to that observed for the other 3,3-disubstituted cyclopropenes (Table 3). With the 3,3-dimethoxy derivative only the thermodynamically more stable 1,2-tra s-dialkoxycarbonylcyclopropanes are formed. This can be taken as an indication for a stepwise addition process with an intermediate of highly zwit-terionic character (structure 29 B or 29 C) that can undergo rotational isomerization to form the thermodynamically most stable product, i.e. the tranx-configurated diester. 

A wide range of 3,3-disubstituted cyclopropenes, e.g. the dimethyl and diphenyl derivatives, as well as spiro[2.4]hept-l-ene or 6,6-dimethyl-4,8-dioxaspiro[2.5]oct-l-ene, can thus be reacted with a variety of mono- and disubstituted alkynes. Usually, the chemoselectivity of this cy-clocotrimerization reaction is remarkably high. The norcaradiene derivatives initially obtained are in equilibrium with the valence tautomeric cycloheptatrienes. The equilibrium ratio of the valence tautomers is strongly dependent on the position and kind of substituents, especially those in the 7-position of the newly formed norcaradienes and cycloheptatrienes. When one or two phenyl groups are present in this position, only norcaradiene products can be detected by and NMR spectroscopy at room temperature, whereas in the case of methyl substituents, both valence tautomers are formed in almost equal amounts. When cyclic alkynes, such as cyclooctyne, are employed in the reaction, only norcaradienes are formed regardless of the substituents present in the cyclopropene cosubstrate. ... 

When 3,3-disubstituted cyclopropenes are treated with transition metal catalysts in the presence of carbon monoxide, carbonylated cyclodi- and cyclooligomerization products are obtained either solely or in addition to homo-cyclodi- and homo-cyclotrimers. The carbonylation products 3,3,7,7-tetramethyl-exo-tricyclo[4.1.0.0 ]heptan-5-one (2) and 4-isopropyl-6,6-dimethyl-bicyclo[3.1.0]hex-3-en-2-one (3) are formed as major products from 3,3-dimethylcyclopropene and carbon monoxide with tetracarbonylnickel as catalyst at ambient pressure and 20°C. Increasing the carbon monoxide pressure to 4.5-5.25 x 10" Torr leads to increased selectivity for the formation of 2 which is obtained in 54% yield along with a 24% yield of ketone 3. 

Similar conversions of cyclopropenes can be achieved with other metal complexes. In the presence of trialkylphosphane-modified Pd(0) catalysts, 3,3-dimethylcyclopropene was quantitatively and stereoselectively cyclotrimerized to give 3,3,6,6,9,9-hexamethyl-c ,c/i,/ran -tetra-cyclo[6.1.0.0 0 ]nonane (14). The structure was derived from spectroscopic data and X-ray crystal analysis. The product undergoes thermal rearrangement to form 3,3,6,6,9,9-hexamethyl-trun. -tricyclo[6.1.0.0 ]non-4-ene (15). ° This method has been extended to other 3,3-disubstituted cyclopropenes. ... 

The most important limitation to this synthetic route is that it can only be used for 3,3-disubstituted cyclopropenes. 3//-Pyrazoles that have hydrogen at C3 undergo an essentially irreversible tautomerization to give the 1//-pyrazole. 

Disubstituted cyclopropenes undergo addition to tetraarylcyclopentadienones to produce mixtures of exo- and emfo-adducts in which the endo-isomer predominates (Table 12).187188 The predominance of enr/o-product has been explained in terms of secondary orbital interactions, involving the methylene group of the cyclopropene.147 3-Methyl-3-vi-nylcyclopropene reacted with 2,3,4,5-tetraphenylcyclopenta-2,4-dien-l-one at the cyclopropene double bond and a [4+2] cycloadduct of unspecified stereochemistry was isolated (41% mp 231-234 °C) together with decarbonylated products reaction of 2-oxo-4,5-diphenyl-l,3-bis(methoxycarbonyl)cyclopentadiene with 3-methyl-3-vinylcyclopropene was more complicated and apparently attack occurred at both 71-bonds.1... 

Disubstituted cyclopropenes undergo ring-opening cross-metathesis with certain alkenes under the influence of 6 to produce (3S)-1,4-alkadienes. ... 

This method has been extended to other 3,3-disubstituted cyclopropenes The structure of 29 which has primarily been derived from spectroscopic data has been... 

Gold(I)-catalysed ring-opening of 3,3-disubstituted cyclopropenes (249) with thiols, thiophenols, and thioacids has been shown to occur regio- and chemo-selectively, producing either vinyl thioethers (250) or primary allylic thioesters (251), depending on the ligands coordinated to Au and the nature of the nucleophile. ... 

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