Cyclopropenes ring syntheses with

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. 

Cyclopropenes cycloaddition-ring opening with - 32, 630 diene synthesis with -30, 469s31... 

Similarly, zincated hydrazone derivatives of type 56 undergo an intermolecular carbozincation of strained cyclopropene rings such as 57 leading to the adduct 58 with 92% yield [63]. This type of addition can be extended to ethylene ]63c]. It proceeds with an excellent stereoselectivity allowing the enantioselective synthesis of a-substituted ketones. Allylic zinc species also add to cyclopropenone acetals... 

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)... 

The synthesis of cycloproparenes resulting from formal fusion of a cyclopropene to furan and thiophene has been attempted with limited success. Reaction of the dichloro-oxabicyclohexane 180 (X = O) " afforded a cyclopropene 181 which ring-opened to a vinylcatbene 182, but the cycloproparene 183 was not produced. Similarly, the thia-analogue 180 (X = S) could not be converted to 184. The intermediate cyclopropenes and/or vinylcarbenes have been trapped. A cyclopropathiophene derivative 186 was generated, however, from 185. Although it was not isolable, it afforded a bis-adduct 187 when it was produced in the presence of isobenzofuran (45)." ... 

In contrast to considerations of 50 years ago, today carbene and nitrene chemistries are integral to synthetic design and applications. Always a unique methodology for the synthesis of cyclopropane and cyclopropene compounds, applications of carbene chemistry have been extended with notable success to insertion reactions, aromatic cycloaddition and substitution, and ylide generation and reactions. And metathesis is in the lexicon of everyone planning the synthesis of an organic compound. Intramolecular reactions now extend to ring sizes well beyond 20, and insertion reactions can be effectively and selectively implemented even for intermolecular processes. 

This method constitutes a convenient synthesis of substituted tricyclo[2.2.0.02,6]hexane derivatives. It is surprising that the ring strain associated with these derivatives would permit their preparation at such high temperatures. A homologous reaction involves the intramolecular [2 + 2] cycloaddition of 2-vinylphenyl substituted cyclopropenes 5 which give benzotricy-clo[3.2,0.02,7]heptenes 6.74 This reaction also proceeds by sensitized photolysis but gives a more complex mixture. 

Functionalized cyclopropenes are viable synthetic intermediates whose applications [99.100] extend to a wide variety of carbocyclic and heterocyclic systems. However, advances in the synthesis of cyclopropenes, particularly through Rh(II) carboxylate—catalyzed decomposition of diazo esters in the presence of alkynes [100-102], has made available an array of stable 3-cyclopropenecarboxylate esters. Previously, copper catalysts provided low to moderate yields of cyclopropenes in reactions of diazo esters with disubstituted acetylenes [103], but the higher temperatures required for these carbenoid reactions often led to thermal or catalytic ring opening and products derived from vinylcarbene intermediates (104-107). 

The 7,7-dihalobicycloheptene route appears easily adaptable to the synthesis of 6n 5 atom cyclopropa[c]heteroarenes 61 as the three-membered ring is suitably located and the requisite precursors—the dichlorocarbene addition products of, for example, 2,5-dihydrofuran—are easily accessible. Unfortunately, treatment of halides 59 with r-BuOK fails to provide any evidence for sought after 61. Dehydrochlorination does occur but the strained 1,3-bridged cyclopropenes 60 ring expand to carbene or add a nucleophile faster than rearrangement and loss of a second molar equivalent of HCl. The precise outcome of these reactions is very dependent upon the nature of the ring system as the detailed studies show . ... 

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