Carbon radical generation

In the next example, the strategy for the formation of fused cyclic ethers utilized the formation of an intermediate a-heterosubstituted carbon radical, generated by the reaction of (TMS)3Si radical with A-(ethoxycarbonyl)-l, 3-thiazolidine derivative [38]. This intermediate gives intramolecular C — C bond formation in the presence of proximate 1,2-disubstituted double bonds (Reaction 7.27). However, when terminal double bonds are used, the hydrosily-lation of the double bond by (TMS)3SiH can compete with the reduction and prevent forming the desired C—C bond formation. 

SCHEME 10. Preparation of hydroperoxides via oxygenation of carbon radicals generated from iV-hydroxypyridine-2-thione esters as radical precursors... 

Organic radical chemistry in synthesis has truly blossomed in the past two decades, and more dramatic advances are expected given the vast scope of synthesis. Radical methodology is attractive because typical conditions for carbon-radical generation and functionalization do not require protection of alcohol and carbonyl functionality... 

Thioethers have also been prepared on cross-linked polystyrene by radical addition of thiols to support-bound alkenes and by reaction of support-bound carbon radicals (generated by addition of carbon radicals to resin-bound acrylates) with esters of l-hydroxy-l,2-dihydro-2-pyridinethione ( Barton esters Entry 6, Table 8.5). Additional methods include the reaction of metallated supports with symmetric disulfides (Entries 7-9, Table 8.5) and the alkylation of polystyrene-bound, a-lithiated thioani-sole [65],... 

The intermediate a-heterosubstituted carbon radicals generated by reaction of (TMS)3Si radical with 1,3-dithiane28, or A-(ethoxycarbonyl)- , 3-thiazolidinc76 derivatives, can participate in consecutive intramolecular C—C bond formation reactions in the presence of proximate 1,2-disubstituted double bonds (equation 51). In the presence of terminal double bonds or in an attempted intermolecular addition of the intermediate... 

Reaction of the unsaturated bromoethyl glycoside 216 in the foregoing manner gives the bicyclic product 217,218 and similar treatment of the propargyl ether 219 with a tributyltin radical results in carbon-radical generation and cyclization to afford the tin-containing adduct 220 in 90% yield. On oxidation with osmium tetraoxide and periodate ion, the Sn-C bond is cleaved, and the corresponding ketone 221 is produced in excellent yield.219... 

A detailed study of the mechanism of nitrite photolysis15 confirmed the ideas used to conceive the existence of the reaction. The carbon radical generated by the photolysis is free because it can be captured by radicophylic reagents permitting other substituents1617 to be introduced at C18. 

Fig. 5.10 Addition to the 5-meso position of the prosthetic heme of the carbon radical generated when HRP oxidizes a diazene (RN=NH). The diazene is itself generated by peroxidatic oxidation of the precursor hydrazine (RNHNH2)...

Diisopropyl tellurium intercepted primary carbon radicals, generated by the photolysis of acyl derivatives of iV-hydroxy-2-thiopyridone, and released isopropyl radicals that were trapped by olefins2. 

Cekovic, Z. Reactions of 5-carbon radicals generated by 1,5-hydrogen transfer to alkoxyl radicals. Tetrahedron 2003, 59, 8073-8090. 

Scheme 5.29 Addition of a carbon radical generated from an N-acyliminium ion pool to an electron-deficient olefin...

Carbon radicals generated by the polymerization of methyl methacrylate do not undergo displacement reactions with the Sn-S, Sn-O, Sn-C, or Sn-Cl bonds of typical organotin stabilizers (73). However, PVC stabilization caused by scavenging of chlorine atoms by organotins has not been ruled out experimentally (73). Furthermore, the ability of... 

Carbon radicals generated by the addition of enol radicals derived from 1,3-dicarbonyl compounds to alkenes are efficiently trapped by oxygen in a chain reaction leading to hemiperacetals [51], The process is illustrated by the electrochemical or AIBN-initiated reaction of 2-methyl-1,3-cyclopentanedione with styrene and oxygen in acetonitrile, which provides the thermodynamically favored all-c bicyclic peroxide in good yield (Scheme 23) [51],... 

Carbon radical generation. Radicals that are formed during dehalogenation can be intercepted intramolecularly by a C=C bond " or C=N bond. A cyclopen-tene synthesis from 1,1-dihaloalkenes apparently involves two-stage reduction, which is intervened by hydrogen abstraction. 

Carbon-Carbon Bond-Forming Reaction via Catalytic Carbon Radicals Generation Assisted by NHPI 223... 

Radical amination. - A radical reaction has been developed to effect the replacement of a hydroxy-group by an amino-group. For example, the carbon radicals generated fnim either the xanthate 13 or anisyltelluride 14 can be trapped by the diazirine 15 (Scheme 5). The resulting imine 16 was hydrolysed to the amine 17. ... 

Carbon radicals generated as a result of triethylborane autooxidation (Scheme 146) react with ICH2C02Et or BrCH(CH3)C02Et in DMSO to produce new radicals capable of reacting with thiophene [210]. 

Umek, R Seo, J. W. Hernadi, K. et al., Addition of Carbon Radicals Generated from Organic Peroxides to Single Wall Carbon Nanotubes. Chem. Mater. 2003,15, 4751-4755. 

T. Iwahama, S. Sakaguchi, Y. Ishii, Catalytic a-hydroxy carbon radical generation and addition. Synthesis of a-hydroxy-y-lactones from alcohols, a,p-unsaturated esters and dioxygen, Chem. Commun. (2000) 613-614. 

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