Cyclopropenyl derivatives

Semiempirical (PM3) and ab initio (6-3IG basis set) calculations are in agreement with the hypothesis described in Section I (99MI233 OOOJOC2494). In the case of the sensitized reaction, when the excited triplet state is populated, only the formation of the radical intermediate is allowed. This intermediate can evolve to the corresponding cyclopropenyl derivative or to the decomposition products. In a previously reported mechanism the decomposition products resulted from the excited cyclopropenyl derivative. In our hypothesis the formation of both the decomposition products and the cyclopropenyl derivatives can be considered as competitive reactions. 

The irradiation of 2,5-dimethylfuran in the presence of mercury vapor gave a complex mixture of products. Carbon monoxide and propene were removed as gaseous products. Then, cis- and rran.s-l,3-pentadiene, isoprene, 1,3-dimethylcyclopropene, 2-pentyne, 2-ethyl-5-methylfuran, hexa-3,4-dien-2-one, 1-methyl-3-acetylcyclopropene, and 4-methylcyclopent-2-enone were obtained (Scheme 8) (68JA2720 70JA1824). The most abundantproduct was the cyclopentenone 19, the second was the 1,3-pentadiene 12, while the third product was the cyclopropenyl derivative 18. 

The formation of 26 can be explained on the basis of the mechanism depicted in the Scheme 11, where the irradiation of the cyclopropenyl derivatives 28 induces a radical reaction to give 26. 

Also in this case theoretical calculations are in agreement with experimental results. In fact, the triplet state of 20 can be converted into the corresponding biradical to give the cyclopropenyl derivative (Fig. 3) (OOOJOC2494). 

Also in this case calculation results fit the experimental data (Fig. 7) [99H(50)1115]. In fact, the singlet excited state can evolve, giving the Dewar thiophene (and then isomeric thiophenes) or the corresponding excited triplet state. This triplet state cannot be converted into the biradical intermediate because this intermediate shows a higher energy than the triplet state, thus preventing the formation of the cyclopropenyl derivatives. 

The most common method to prepare cyclopropenyl derivatives is the reaction between an electrophilic carbenoid and an alkene. On the other hand, sp3-geminated organodimetal compounds possess two nucleophilic sites on the same carbon, so should lead to nucleophilic [2+ 1] reaction with 1,2-diketones. Indeed, the reaction of bis(iodozincio)methane (3) with 1,2-diketones shows a novel [2+1] reaction to form c -cyclopropanediol diastereoselectively as shown in Scheme 3467. 

An attempt has been made to extend the discussion to the unsaturated derivatives of cyclopropane, i.e cyclopropene and methylenecyclopropane however, the treatment is not extensive either due to a paucity of pertinent chemistry or to coverage elsewhere in this volume (Cyclopropenes, Chapter 21 Cyclopropenyl derivatives. Chapter 24). The reader will also note that the discussion on basicity of cyclopropanes is considerably more extensive due to the wealth of new chemistry and conceptualizations in the past dozen or so years. 

This chapter describes the electrochemical formation of the cyclopropyl ring both in fused and non-fused systems, by anodic and cathodic processes. The electrochemical properties of cationic cyclopropyl and cyclopropenyl derivatives are surveyed, as well as those of related compounds such as bicyclobutanes, cyclopropanones, cyclopropanols, cyclopro-penones, etc. All quoted electrochemical potentials are related to SCE and corrected... 

Strong interaction between its double bonds through interaction between C(3) and C(3 )5i,52 Discussions of cyclopropenes and aromatic cyclopropenyl derivatives are presented in Chapter 21 by Halton and Ban well, and in Chapter 24 by Billups and Moorehead. 

As deduced from low temperature ESR characterization [72], as well as theoretical studies [73], cyclopropenyl radicals 3C adopt a totally different cr-radical structure. The spin density is located at one of the carbon centers, which is in a strongly pyramidal environment. Accordingly, dimerization of such radicals proceeds by cr(C-C) coupling to give bis (cyclopropenyl) derivatives 29 [74] (Fig. 12). 

Upon photolysis in an acidic aqueous solution, 1,2,3-triphenylcyclopropenylium ion 1 underwent an electron transfer yielding the cyclopropenyl radical. Facile radical coupling then led to the bi(cyclopropenyl) derivative, which photochemically rearranged to hexaphenylbenzene 15 3.154 contrast, the 1,2-dipropylcyclopropenylium ion, which requires much higher ex-... 

The above cyclopropenyl derivative, related compounds, and germanium analogues (see p. 202) are obtained from the well-known thermal difluoro-carbene source McsSn CFa and the corresponding alkynes Me Sn-... 

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