Azo-n-propane

Stereochemically controlled synthesis of this subunit, which contains five stereogenic centers, is important to an efficient bleomycin synthesis. (2S,3S,4i )-4-(/er/-Butoxycarbonyl-amino)-3-hydroxy-2-methylpentanoic acid (15) was obtained via a stereoselective syn aldol addition of a boron Z-enolate with (27 )-2-(tert-butoxycarbonylamino)propanal (Scheme 4). Similarly, the L-threonine subunit 18 was prepared by diastereoselective syn aldol addition of an N- acy I ox azo I i di n one stannous Z-enolate with acetaldehyde. The bithiazole unit 19 was prepared using a direct DCC-promoted condensation of 3-(methylsulfanyl)propylamine. Convergent access to tetrapeptide S was obtained by coupling of acid 15 and deprotected 18 to give dipeptide 20, followed by further coupling with the bithiazole 19 to ultimately give tetrapeptide S (21). 

Azobis (2-methyl-N-phenylpropionamidine) dihydrochloride 2,2 -Azobis (2-methylpropane) 2,2 -Azobis (2-methylpropionamide) dihydrate 2,2 -Azobis [N-(2-propenyl)-2-methylpropionamide] 2,2 -Azobis [2-(3,4,5,6-tetrahydropyrimidin-2-yI) propane] dihydrochloride 2,2 -Azobis (2,4,4-trimethylpentane) n-Butyl-4,4-bis (t-butylperoxy) valerate t-Butyl hydroperoxide t-Butyl peroxycrotonate t-Butyl peroxyneoheptanoate Cerium Cumene hydroperoxide Cumyl peroxyneodecanoate o-Cumylperoxyneoheptanoate 1 -[(1 -Cyano-1 -methylethyl) azo] formamide Decanoyl chloride Decanoyl peroxide Di-t-amyl peroxide 2,2-Di (t-butylperoxy) butane Dicetyl peroxydicarbonate Dicyclohexyl peroxydicarbonate Dimethyl 2,2 -azobis (2-methylpropionate) 2,5-Dimethyl-2,5-di (benzoylperoxy) hexane 2,5-Dimethylhexane-2,5-dihydro peroxide Dimyristyl peroxydicarbonate Di-n-propyl peroxydicarbonate Ethyidibutylperoxybutyrate 3,3,6,6,9,9-Hexamethyl 1,2,4,5-tetraoxa cyclononane Lauroyl chloride Pelargonyl peroxide, 2-Phenylazo-4-methoxy-2,4-dimethylvaleronitrile Phosphine Potassium persulfate Sodium persulfate Succinic acid peroxide... 

Other azo initiators have been used in C-enriched forms, namely azobis-1, T-phenylethane (APE), Me CHPh-NrN CHPh-Me, l,l -azobis( 1,3-diphenyl-propane), Ph CH2 CH2 CHPh N N CHPh CH2 CH2-Ph and 4,4 -azobis-(4-phenylbutyronitrile), CH2(CN)-CH2 CHPh-N N CHPh CH2 CH2 CN. These compounds are of little practical importance as initiators of polymerization but they give rise to radicals with structures that are of great interest for studying the factors influencing the reactivities of radicals towards monomers. 

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