Zirconium-induced reactions

As shown in the proceeding sections, the aldol reaction - especially in a domino fashion - is one of the most suitable procedures for C-C-bond formation. Usually, one uses an enolate and a carbonyl moiety, but allylic alcohols can also be em- 

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By using the hypersensitive molecular mechanistic probe 2-(2-methoxy-3-phenylcy-clopropyl)-5-methylhexa-2,4-diene in the 2 + 2-photocycloaddition of [60]fullerene, it was shown that the reaction proceeds via a biradical and not a dipolar intermediate.6 Zirconium-induced cyclodimerization of heteroaryl-substituted alkynes produces tetrasubstituted cyclobutenes with high regio- and stereo-selectivity.7 The ruthenium-... 

Organozirconium compounds are attractive intermediates in an impressive array of synthetic methodology and have received much attention in recent years [14], Among various possibilities for the generation of organozirconium reagents, low-valent zirconium-induced (3-alkoxide elimination reaction is a particularly attractive protocol. 

Berg FJ, Petersen JL (1989) Reactivity studies of the zirconium-induced insertion of isonitriles into a l-sila-3-zirconacyclobutane ring. Stmctural and chemical evidence of carbenium-like intermediates for the intramolecular 1,2-silyl shift and reductive coupling reactions. Organometallics 8 2461-2470... 

The reactions of various 2-butenyltitanium and -zirconium reagents with 2-(benzyloxy)propanal (and other O-protected derivatives) also proceed with low induced diastereoselectivity90. 

Rac/meso-isomers of bridged bis(indenyl) zirconium dichlorides can interconvert photochemically.796 This interconversion has been utilized in the stereoselective synthesis of ansa-zirconoccnc binaphtholate stereoisomers.797 Specifically, the rac-meso-mixtures 1034 induced by irradiation in toluene react with 1 equiv. of the dilithium salt of racemic binaphthol to give the racemic binaphtholate complex 1035 (Scheme 253). Analogous reactions with 1 equiv. of the Z (+) enantiomer of dilithium binaphtholate afford the enantiomerically pure binaphtholate complex. The structure of the racemic binaphtholate complex, Me2Si(2-Me-4-But-C5H2)2Zr(binaphtholate), has been crystallographically determined. 

The metal component of catalysts, solvent selection, and reaction concentration can influence aggregation and affect reactivity. The titanium catalyst 13 forms monomeric complexes in solution, but the analogous zirconium catalyst 14 forms polynuclear aggregates (Figure 9.7) this may explain why the chirality induced by oxidation of the sulfides is opposite for these two catalysts [23]. 

A variety of cation-induced cyclization approaches to systems of this type have been introduced. Reaction of hydroxyethylthiocyanates (236) with a tertiary alcohol, R OH, in sulfuric acid gives the 2-iminooxathiolanes (237) (Equation (35)) <92Z0R418> and treatment of glycidyl esters such as (238) with cationic zirconium complexes such as (239) and AgC104 gives the dioxolane (240) (Equation... 

Titanium, Zirconium, and Hafnium.—Several reports on the photochemistry of titanocene derivatives have appeared this year. Harrigan et e/.180 observed that the photolysis ( > 480 nm) of Cp2TiCI2 in chlorinated hydrocarbons gave CpTiCl3, and they proposed that light-induced cleavage of the Ti-Cp bond occurs, as in reactions (57) and (58). In support of this mechanism, photo-... 

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