Substituted cyclopropenes, ring opening

The synthesis of cyclopropanes via cyclopropene ring opening with subsequent [1 +2] cycloaddition is restricted to thermolytically or photochemically initiated, and transition metal catalyzed reactions, and furthermore is only applicable to suitably substituted alkenes. 

A thermal ring opening reaction of an imine-substituted cyclopropene led to a mixture of 2,3,4-trisubstituted and 3,4,5-trisubstituted pyrroles <06TL5793>. 

The dichlorocarbene adduct 148 of 9-methoxyphenanthrene eliminates HCl instead of MeOH and forms a cyclopropene 152, Ring-opening produces the substituted vinylcarbene 154. The latter inserts intramolecularly into the methoxy group and, after elimination of HCl from 157, a phenanthrofuran 158 is obtained. The sequence is applicable to substituted furans and even to phenanthrocyclopen-tadienes. ... 

Silyl-substituted cyclopropenes have been observed to rearrange photochemically giving high yields of allenes. A typical example is shown in equation 2 where the silylcyclo-propene 3 apparently ring-opened to the carbene 4 which, following 1,2-silyl migration, led to the allene 513. 

Saito reported the extension of Billups tandem silver-catalyzed ring-opening cycloaddition reaction methodology to addition to imines (Scheme 2.45).77 Naphtho- /) cyclopropene 167 added to substituted aryl imines 168 at room temperature in the... 

The most strained cycloolefins, which are substituted cyclopropenes, e.g. 3,3-dimethylcyclopropene or 3-methyl-3-ethylcyclopropene, appeared to be polymerised readily to respective substituted poly(l,2-cyclopropene)s in the presence of Pd-based catalysts containing very bulky non-labile ligands. Such catalysts are characterised by reduced activity in order to prevent ring opening of the cyclopropene monomer [23],... 

Ring opening of 1,3- and 1,2-disubstituted cyclopropenes has also been examined. The ester (194) rearranges on heating to 98 °C in the presence of copper to give furan (195) the less substituted cyclopropene single bond appears to be cleaved to produce a carbene-metal derivative, which cyclises to the ester group 136). A similar photochemical transformation of a cyclopropene-3-ester to a fiiran has already been described 115). 

Indenyl complexes of Pd are prepared by the reaction of indenyl sodium with anhydrous PdCl2. Alternatively, they are available by ring-opening reactions of aryl-substituted cyclopropenes with PdCl2(PhCN)2 (equation 49). 

The comparison of the ionization potentials of identically substituted cyclopropenones, cyclopropenes and cyclopropanes is interesting, if not yet particularly informative to date. The ionization potentials of cyclopropane, cyclopropene and cyclopropenone are much closer, 9.86, 9.67 and 9.47 eV, than for their diphenyl derivatives. Diphenylcyclopropene has an adiabatic ionization potential of 7.45 eV while those of the cis and trans isomers of 1,2-diphenylcyclopropane (18) are 8.20 and 8.05 eV respectively. These latter values for the saturated species correspond to ring-opening to l,3-diphenylprop-l-yl-3-ium (19) (equation 24) a result corroborated by both experiment via solution phase chemi-ionization and ab initio calculations on the analogous divinylcyclopropane. (The... 

Addition of bromine to a number of other cyclopropenes is reported to lead only to ring-opened or ring-expanded products. This reaction is highly dependent on the substitution thus... 

Oxymercuration of simple alkyl- and acyl-substituted cyclopropenes generally results in ring opening.Addition of mercury(II) acetate to 3-methyl-3-phenylcyclopropene, however, gave a low yield of a cyclopropane containing organomercury compound (15-20%), which was converted into an isomeric mixture of 1 -methoxy-2-methyl-2-phenylcyclopropanes by reduction with lithium aluminum hydride. Reaction of 5 with mercury trifluoroacetate in methanol and then sodium hydroxide led predominantly to one cylopropane. ... 

By analogy, the 3-methoxycarbonyl-l-propylcyclopropene ring opens under copper catalysis and can react with strained alkenes.Bisdonor-substituted cyclopropenes, such as 3,3-... 

The addition of a range of nucleophiles to the fluorenyl-substituted cyclopropene 3 led to the formation of the products 4 resulting from ring opening. ... 

Palladium.—[Pd(Cl)2(PhCN)2] reacts with phenyl-substituted cyclopropenes via ring-opening to give y -allyl complexes (14) according to Scheme 9. The influence of... 

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