Chiral titanium complexes for enantioselective addition of nucleophiles to carbonyl groups

Article Abstract:

Chiral titanium complexes can mediate the addition of carbon nucleophiles to carbonyls via two mechanisms. For d(sup 1)-nucleophiles, the favored path involves a six-center transition, with a third mediator molecule from the d(sup 1)-reagent (usually a methyltitanium) serving as catalyst. The second path passes throough a bimolecular six-center cyclic transition for d(sup 3)- nucleophiles, using allyltitaniums or titanium enolates. The reagents are obtained by substituting protic ligands for Ti-boundchlorides or by transesterification of titanium alkoxides with a free alcohol. The various synthetic strategies and uses of the reagents are discussed.

Usage, Chirality, Titanium compounds

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Coupling of organic halides with carbonyl compounds promoted by SmI(sub 2), the Kagan reagent

Article Abstract:

The proper choice of conditions can modulate the high reducing ability of Samarium diiodide (SmI(sub 2)). SmI(sub 2) is soluble in tetrahydrofuran and does not require tedious activation or special manipulations. Stepwise chemoselective reductions can be affected by SmI(sub 2). The use of coadditives or visible light allows for the proper tuning of its reducing ability. The reactions offer the advantage of producing organometallic radicals in the end.

Chemical tests and reagents, Reagents, Halides

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The chemistry of thietane ligands in polynuclear metal carbonyl complexes

Article Abstract:

Thietanes with lone pairs on the sulfur atom act as stable ligands in the polynuclear metal carbonyl complexes. One or two of the lone pairs are coordinated to the metal atoms serving as terminally coordinated or bridging thietane ligands respectively. The thietane ligands undergo ring opening and cyclooligomerization transformations. Cyclooligomerization of thietanes generate polynuclear metal carbonyl complexes with macrocycles.

Cyclic compounds, Ligands, Ligands (Chemistry)

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