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Organometallic Compounds of Titanium and Zirconium as Selective Nucleophilic Reagents in Organic Synthesis
Author(s) -
Weidmann Beat,
Seebach Dieter
Publication year - 1983
Publication title -
angewandte chemie international edition in english
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.831
H-Index - 550
eISSN - 1521-3773
pISSN - 0570-0833
DOI - 10.1002/anie.198300311
Subject(s) - chemistry , benzaldehyde , acetophenone , reagent , transmetalation , allylic rearrangement , zirconium , reactivity (psychology) , metalation , nucleophile , enantioselective synthesis , organic chemistry , medicinal chemistry , ketone , umpolung , catalysis , medicine , alternative medicine , pathology
Abstract The addition of carbanionic organometallic compounds (usually RLi or RMgX) to a carbonyl group—a key step in numerous syntheses—is not always straightforward. Depending on the substrate, various complications and problems may arise, but in many cases these can be remedied by addition of (RO) 3 TiCl, (RO) 3 ZrCl or (R 2 N) 3 TiX to the classic lithium and Grignard reagents. This usually leads to formation of stable organo‐titanium and ‐zirconium compounds which react highly selectively with carbonyl groups. For example, CH 3 Ti(O i Pr) 3 reacts five orders of magnitude faster with benzaldehyde than with acetophenone at room temperature; reagents of the type RTi(O i Pr) 3 add smoothly to nitro‐, ido‐, or cyano‐subsituted benzaldehyde, and the reactions may be performed in chlorinated solvents or acetonitrile; the zirconium analogues have particularly low basicity and add in high yield to α‐ and β‐tetralones or to substrates containing a nitroaldol group; the inclusion of chiral OR * groups gives enantioselective reagents (up to 90% ee ); allylic (RO 3 )Ti‐ derivatives react only at the more highly substituted carbon atom and, in addition, react diastereoselectively (up to 98% ds ) with unsymmetrical ketones. Finally, titanium reagents have also been found to effect novel transformations such as direct geminal dialkylation (CO→CMe 2 ) and alkylative amination [CO→CR(NR   2 ′ )]. The modification and finetuning (“taming”) of carbonyl reactivity obtainable by use of the new reagents is not dearly bought; starting materials are the cheap and harmless “titanates”, “zirconates” and the corresponding tetrachlorides.

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