Methyl radicals cyclo

Charge acceleration has also been observed in the rearrangement of 2-allyloxy-2-cyclo-hexenones. In comparison to the silyl enol ether derivative of 2-allyloxy-3-methyl-2-cyclo-hexenone, the lithium cuprate derivative obtained by conjugate addition of lithium dimethyl-cuprate rearranges much faster. This effect has been explained by the intermediacy of an allyl radical/oxyoxaallyl radical anion (semi-dione) pair84. 

Addition of P—H bonds to unsaturated systems also continues to be used as a route to heterocyclic systems. Thus base-catalysed cyclization of the phosphine (32) [prepared by the addition of methyl methacrylate (2 moles) to phenylphosphine], followed by subsequent hydrolysis and decarboxylation, affords the phosphorinanone (33). The phosphorinanone system is also directly accessible by the addition of phenylphosphine to divinyl ketones.28 The radical-initiated addition of phenylphosphine to dialkynyl systems (34) gives the heterocyclohexadienes (35).29 80 The stereochemistry of the addition of phenylphosphine to cyclo-octa-2,7-dienone to give... 

Two possible mechanisms are proposed. Primarily the enol radical cation is formed. It either undergoes deprotonation because of its intrinsic acidity, producing an a-carbonyl radical, which is oxidized in a further one-electron oxidation step to an a-carbonyl cation. Cyclization leads to an intermediate cyclo-hexadienyl cation. On the other hand, cyclization of the enol radical cation can be faster than deprotonation, producing a distonic radical cation, which, after proton loss and second one-electron oxidation, leads to the same cyclo-hexadienyl cation intermediate as in the first reaction pathway. After a 1,2-methyl shift and further deprotonation, the benzofuran is obtained. Since the oxidation potentials of the enols are about 0.3-0.5 V higher than those of the corresponding a-carbonyl radicals, the author prefers the first reaction pathway via a-carbonyl cations [112]. Under the same reaction conditions, the oxidation of 2-mesityl-2-phenylethenol 74 does not lead to benzofuran but to oxazole 75 in yields of up to 85 %. The oxazole 75 is generated by nucleophilic attack of acetonitrile on the a-carbonyl cation or the proceeding enol radical cation. 

The intramolecular cyclization dominates other possible reactions even in solvents highly susceptible to free radical attack (110). Thus, irradiation of 4,5-octanedione in butanal gives 2-hydroxy-3-methyl-2-propylcyclobutanone in 92% yield (110). Irradiation of 1,2-cyclo-decanedione (Formula 264) gives 1-hydroxybicyclo [6.2.0 ]decan-10-one (Formula 265) in 74% yield and cyclooctanone (Formula 266) in 9% yield (111). The cyclooctanone is produced together with ketene by a secondary photolysis of Formula 265 (111). 

If the nitro group is located at the ethylenic fragment, one-electron transfer initiates dimerization of the developing anion radicals. a-Nitrostilbene, w-methyl-w-nitrostyrene, and a-nitro-(3-ferrocenylethylene give anion radicals that dimerize spontaneously. It is interesting to compare reactions of cyclo-octatetraene dipotassium (C8H8K2) with a-nitro... 

However, through quartz at 95% conversion, a mixture of I (62%) and l-carboxymethyl-2-phenylcyclooctatetraene (IT) (38%) was obtained. Compound n could be obtained exclusively (92%) from triplet-sensitized irradiation of I with high-energy sensitizers or from the sensitized reaction of methyl phenylpropiolate with benzene. From their experiments with sensitizers, the authors concluded that the primary adduct is formed from triplet alkyne (ET < 69 kcal/mol 1) and ground-state benzene and that the formation of I also proceeds via a triplet state in a two-step radical reaction. Hanzawa and Paquette [64] have also used the photochemical addition of an alkyne to benzene to produce a derivative of tetra-cyclo[3.3.0.02,4.03 6]oct-7-ene. 

Irradiation at 350 nm of 1,1-dibromocyclopropanes dissolved in liquid ammonia or dimethyl sulfoxide in the presence of sodium benzenesulfanate leads to l,l-bis(phenylsulfanyl)cyclo-propanes. The yields are in all cases below 50% which is due to both decomposition of the product on longer irradiation and formation of significant amounts of cyclopropyl phenyl sulfide. Most 1,1-dichlorocyclopropanes are unreactive, and no reaction occurs in the presence of oxygen, di- erf-butyl nitroxide and 1,3-dinitrobenzene, which supports the notion that the reaction is a radical process. The cleanest reaction took place during irradiation of 2,2-dichloro-1 -methylcyclopropanecarbonitrile, which gave no sulfide, little unreacted starting material, and 1-methyl-2,2-bis(phenylsulfanyl)cyclopropanecarbonitrile (4) in 47% yield. 

Free-radical epimerisation of unactivated tertiary carbon atoms by irradiation in cyclohexane containing 1 equivalent of mercuric bromide has been demonstrated in both cyclo-pentanes and -hexanes. Thus, 5/S-androstane gives 95 % 5, 14 -androstane after irradiation for 12 hours. Irradiation for longer periods gives up to 70% of the 5a,14jS-androstane. Similarly, irradiation of 3, 11 P-diacetoxy-4 -methyl-5a-androstane led to quantitative epimerisation and the formation of the 4a-methyl-14 -isomer. ... 

The allylsulphonium salt (209) is recommended as a synthetic equivalent of the unstable allyl trifluoromethanesulphonate. Treatment of methyl diazoacetate with an excess of thiobenzophenone yields a mixture of the dithioles (210) and (211) by way of the thiocarbonyl ylide Ph2C=S—CHCO2-Me. The resistivities and magnetic susceptibilities of the radical-anion salts (212 R, R = H, Me, or Ph n = 1 or 2) have been measured. The meso-ionic 1,3-dithiolium 4-oxide (213) forms the intramolecular cyclo-adduct... 

In morphine (agonist), the replacement of the A-methyl group by a more bulky radical such as A-allyl, A-cyclo-propyl-methyl or A-cyclobutyl-methyl leads to powerful antagonists of the opiate receptors (see Chapter 19 Unsaturated Groups). 

Wong (1981) studied the competition between the self-reaction of t-C4H90 radicals and the reaction of r-C4H90 with several hydrocarbons in solution at 293 K. He used a flash-photolysis system with electron-spin-resonance detection of the radicals to measure the competitive reactions. Based on his earlier results for the hydrocarbon rate coefficients (Wong, 1979), he deduced the rate coefficient for the self-reaction to be (1.3 0.5) x lO A/ -sec at 293 K. The hydrocarbons used in the competitive experiments were cyclo-pentane, anisole, methyl-terr-butylether, and methanol, with respective rate coefficients for reaction with I-C4H90 of 3.4 X 10 , 7.2 x lO, 2.43 x 10 , and 1.29 x 10 M -sec . ... 

Bennasar extended his research on 2- and 3-indolylacyl radicals to intramolecular cyclizations to yield 2,3-fused indoles [112], Under nomeductive conditions (n-Bu6Sn2, hv), radical 201 underwent a cascade addition-oxidative cyclization sequence with a number of alkene acceptors including dimethyl fumarate (45%), methyl 1-cyclohexenecarboxylate (53%), methyl crotonate (71%), vinyl sulfone (22%), and the a,p-unsaturated lactam ester, 2-oxo-5,6-dihydro-2H-pyridine-l,3-dicarboxylic acid dibenzyl ester (41%) to form cyclopenta[h]indol-3-ones 202. Reaction of 201 with acrylonitrile and methyl acrylate, however, generated cyclo-hepta[h]indoles, the products of bis-addition-cyclization sequences. 

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