Lead reagent

BF, or BF3 etherate can replace TiCl4 as the Lewis acid. But in order to effect clean reactions, the Lewis acid should be added to the aldehyde before addition of the lead reagent. The rate of reaction is highly dependent on the size of the R group. Transfer of an ethyl group is rapid, but a cyclohexyl group is transferred slowly even at 0°. Similar transfer does not obtain with R4Sn. 

Hiickel band calculations, rigid-rod transition metal-acetylide polymers, 12, 371-372 Human health, tin toxic effects, 12, 637 Hybrid magnets, metallocene-containing bimetallic M(II)—Cr(II) oxalates, 12, 427 bimetallic M(II)-Fe(III) oxalates, 12, 432 bimetallic M(III)-Ru(III) oxalates, 12, 435 materials, 12, 437 properties, 12, 425 trimetallic oxalates, 12, 436 Hydantoins, with lead reagents, 3, 888 Hydration... 

Iodo dimethyl amido complexes, with Ti(IV), 4, 331-332 Iodonium salts, cross-coupling with lead reagents, 9, 413 Ionic addition reactions, mechanisms, 1, 101 Ionic bis(isonitrile) complexes, liquid crystals, 12, 280 Ionic character, organometallic compound dn configuration,... 

Lead(IV) acetate is most commonly employed to plumbylate arenes, often using chloroform as the solvent. Being a relatively weak electrophile, Pb(OAc)4 can react only with electron-rich aromatic compounds, for example anisole and polyalkoxy-benzenes. The electrophilicty of the lead reagent is, however, enhanced substan-... 

The reaction of 4-indolyllead triacetate 12 was explored with a number of /3-ketoesters in a study directed toward the total synthesis of welwistatin D (Scheme 3).26 However, while the model ketone derivatives 13 and 15 could be arylated in high yields with lead reagent 12 to give 14 and 16 respectively, the reaction with the more highly substituted welwistatin precursor 17 failed, probably because of the steric hindrance imposed by the methyl and vinyl substituents. 

O-Arylation of alcohols or phenols cannot be performed by copper diacetate-catalyzed reactions using aryllead triacetates as the source of the aryl ligand. However, Dodonov et at. reported that tetraphenyllead reacts with primary and secondary alcohols in the presence of copper diacetate to afford the derived O-phenyl ethers in moderate yields ranging from 1.25 to 1.8 mol. of ether per mole of the lead reagent (Equation (100)). Phenol and tert-butyl alcohol afforded lower yields of the ethers (0.72-0.95 mole per mole of the lead reagent).117... 

Although these two reactions are similar to the corresponding reactions of arenediazonium salts, aryl radicals are not involved in the reaction of the lead reagents and these reactions are better explained by a ligand coupling mechanism. 

Stereoselective aldol reactions with a-methoxy organolead reactions (cf. 16,242). The a-methoxy lead reagent 1 reacts with 2-phenylpropanal in the presence of TiCU with high diastcrcosclcctivity at three contiguous centers (equation I). Only two of the four possible aldols are formed and these two arc formed in the ratio 95 5. The tin reagent corresponding to 1 shows similar diastereosclectivity, but the total yield is only 19%. 

Table 10.1. Lead Reagent Blank and Total Lead Background Levels...

The a-methoxy lead reagent 1 reacts with 1 with high diastereoselectivity at three coniigi four possible aldols are formed and these two 3 corresponding to 1 shows similar diastereoset... 

A brief screen of potential radical mediators revealed that most oxidants facilitated the tosyl group elimination (Table 4). However, two lead reagents were identified, azobisisobutyronitrile (AIBN) and cumene hydroperoxide (CHP), both of which delivered the product in >80% solution yield, while minimizing over-oxidation. Ultimately, CHP was selected due to its commercial availability and ease of handling—CHP is used in the commercial synthesis of acetone and phenol (via the Hock rearrangement)." ... 

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