Carbanion initial

For leading references see S. Wolfe, L. A. LaJohn and D. F. Weaver, Tetrahedron Letters, 25, 2863 (1984) Cor study of a-lithiosulfinyl carbanion initiated oligomerization, see M. Buese and T. E. Hogan-Esch, J. Amer. Chem. Soc., 107,4509 (1985) for a study of a-lithiosulfinyl carbanion alkylation in a cyclic system, see Y. Tamura, J. Uenishi and H. Ishibashi, Chem. Pharm. Bull., 32, 891 and 898 (1984). 

The autoxidation mechanism by which 9,10-dihydroanthra-cene is converted to anthraquinone and anthracene in a basic medium was studied. Pyridine was the solvent, and benzyl-trimethylammonium hydroxide was the catalyst. The effects of temperature, base concentration, solvent system, and oxygen concentration were determined. A carbanion-initi-ated free-radical chain mechanism that involves a singleelectron transfer from the carbanion to oxygen is outlined. An intramolecular hydrogen abstraction step is proposed that appears to be more consistent with experimental observations than previously reported mechanisms that had postulated anthrone as an intermediate in the oxidation. Oxidations of several other compounds that are structurally related to 9,10-dihydroanthracene are also reported. 

Contrarily to the carbonium ion graft copolymerization, carbanion initiation has been attempted for the synthesis of block copolymers. 

A survey of the literature revealed not many published carbanion-initiated C—C bond fragmentaticHi reaction studies. Closer inspection of this body of... 

Formation of (x,/3-Unsaturated Compounds by Dehydration of Aldol Products. As previously stated, the /9-hydroxy carbonyl product of the aldol condensation is thermod5mamically unfavored at high temperatures. Under these conditions, the /9-hydroxy carbonyl is hardly found among the reaction products because it is readily converted to the corresponding o, y0-unsaturated carbonyl compound by dehydration on acid and bases. However, the dehydration step will only take place if the reactant molecule that supplies the carbanion initially contains a second a-hydrogen, in other words, a methylenic group. Thus, in Scheme 1, at least one of substituents R4 and R5 is required to be a hydrogen atom. 

Phenyl vinyl sulfoxide can be polymerized and randomly oxidized to form sections of phenyl vinyl sulfone (VSO2) before elimination (vide supra) to control the conjugation length of the resulting PA (Scheme XVI) [74]. To a flask containing dry and distilled THF was added a few drops of alkyl lithium (1M solution) to remove any remaining impurities from the solvent. Next, more of the carbanion initiator (0.5 ml of a 1 M solution) was added, and the temperature was lowered to —78°C. The VSO monomer (5 ml) was then added, and the color of the solution turned to... 

The first function is that of a diluent the simultaneous generation of carbanionic initiating/propagating sites and the monomer consumption by the latter can liberate a considerable heat in the reaction medium that can be better removed if a solvent is present. Solvents used as diluents are always aliphatic or aromatic hydrocarbons they do not modify or only to a little extent the structure of active centers. 

ANIONIC GRAFTING PROCESSES 12.4.1 Grafting via Carbanionic Initiation... 

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