Cyclopropenes, synthesis

In a pyrrole synthesis, cyclopropene 85 and a twofold excess of phenylacetonitrile were treated with GaCl3 at 80 °G for 2h. The 1,3-diazepine 86 was formed in 10% yield as a by-product in this reaction (Equation 14)... 

Wang, R., Ksebati, M. B., Corbett, T. H., et al. (2001) Methylene< m-difluorocyclopropane analogues of nucleosides Synthesis, cyclopropene-methylenecyclopropane rearrangement, and biological activity. J. Med. Chem., 44, 4019 4022. 

Cyclopropanes are now readily available and have become useful, through hydrogenolysis, for synthesis of compounds containing quaternary carbons, em-dialkyl, r-butyl, and angular-methyl substituents (779), compounds often available only with difficulty otherwise (.77,5i,55,750,756), Cyclopropanes can be formed in good yields by hydrogenation of cyclopropenes (26). 

An interesting cycloheptatriene (182) synthesis has been described using thiophene 1, 1-dioxides (180) and cyclopropenes 181 (equation 121)ns. Concerted [4 + 2]cycloaddition and subsequent cheletropic extrusion of sulfur dioxide are suggested by the second-order kinetics (first in each reactant), and by the large negative activation entropy. 

Alkenes can add to double bonds in a reaction different from those discussed in 15-19, which, however, is still formally the addition of RH to a double bond. This is called the ene reaction or the ene synthesis For the reaction to proceed without a catalyst, one of the components must be a reactive dienophile (see 15-58 for a definition of this word) such as maleic anhydride, but the other (which supplies the hydrogen) may be a simple alkene such as propene. Cyclopropene has also been used. ° The reaction is compatible with a variety of functional groups that can be appended to the ene and dienophile. N,N-Diallyl amides give an ene cyclization. 

Cycloaddition of the carbene chromium complexes 97 with CO incorporation provides a versatile method for naphthol synthesis, in which the metallacy-clic intermediates 99 are involved [47]. An alternative entry to 101 is achieved by metal carbonyl-catalyzed rearrangement of the cyclopropenes 98 via the same metalla-cyclobutenes 99 and vinylketene complexes 100 [52], Mo(CO)6 shows a higher activity than Cr(CO)6 and W(CO)6. The vinylketene complex 103 is formed by the regioselective ring cleavage of 1,3,3-trimethylcyelopropene 102 with an excess of Fe2(CO)9 [53]. (Scheme 35 and 36)... 

Triafulvene 69 was synthesized by an interesting route starting with diphenyl cyclopropenium cation and lithio ethyl acetate72. Although widely used in calicene chemistry (see later) this reaction principle — like the Wittig reaction — did not find general application in methylene cyclopropene synthesis. 

Their synthesis is possible from (a) condensation of arylmalononitriles and cyclopropenones in acetic anhydride, or (b) thermolysis of A1,2-cyclopropene-3-ethers 114 (adducts of cation 117 and arylmalononitrile anion), as exemplified by 115/116 ... 

A variety of functionalized [3]radialenes have been prepared starting from the appropriately substituted cyclopropanes or cyclopropenes. West and Zecher have pioneered the chemistry of [3]radialenes with quinoid substituents. The general strategy of this synthesis is outlined in Scheme 513. A tris(4-hydroxyphenyl)cyclopropenylium... 

A further proof for the structure of 3a is the independent synthesis of this cyclopropene via intramolecular addition of a carbene carbon atom to the triple... 

CYCLOPROPANECARBOXYLIC ACID, cis-2-PHENYL-, 50, 94 Cyclopropane derivatives, synthesis, 52, 22, 33, 132 Cyclopropenes, 50, 30 Cyclopropenone, di-tert-buty1-,... 

The reactions between cyclopropenes and carbon monoxide in the presence of transition metals have been of some use in synthesis,93 and in 1978 Binger initiated a study of the reactions between metal carbonyls and cyclopropenes in order to elucidate the generality of these reactions.75 It was found that dicarbonyl 775-cyclopentadienyl(tetrahydrofuran)manganese(I) reacted with 3,3-dime thy Icy clopropene at 0°C to produce -(vinylketene) complex 81 in fair yield. The only other transition metal in Binger s study that was found to react with 3,3-dimethylcyclopropene in this manner was iron (see Section VI,B). 

Although the original synthesis of an 774-vinylketene complex1 (see Section VI,B) had used the method of metal insertion into a cyclopropene ring, it was more than 20 years before it was applied to metals such as... 

It was not until 1979 that he improved this synthesis and provided an unequivocal X-ray structure of the product. The cyclopropene is extremely... 

The earliest alternative to cyclopropene insertion as a viable vinylketene synthesis was published by Hoffmann118 in 1972. Upon reaction of 206.a with diiron nonacarbonyl, the vinylketene complex 207 was isolated in low yield. The analogous bromide and iodide substrates formed the 77-allyl complexes 208, although a trace of 207 was isolated from the reaction of the bromide 206.b. 

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