Regioselective Zirconium-Mediated Cross Coupling of N-Methyl-N-propargyl Aniline and Alkenes

Abstract

Regioselective Cross Coupling, Propargylamine-Zirconocene Complex, Zirconacyclopentene N-(2-bromoallyl)-N-methylaniline 1 is easily converted into the propargylamine-zirconocene complex 3 via loss of m ethane from 2-[zirconocene(methyl)]allyl amine 2. Regioselec tive insertion reactions with alkenes and benzophenone afford, after iodinolysis, products 4 -10.Recently the use of zirconium complexes in o r ganic synthesis has been widely recognized [1]. One of the most interesting transform ations which has been developed is the formation of unsatu rated system-metallocene complexes either by di rect complexation between the unsaturated com pounds and zirconocene [2] or by a /3-hydrogen abstraction process [lb, 3] followed by the inser tion of alkynes, alkenes, carbonyl compounds, or nitriles to generate the corresponding zirconacyclopentanoids. A great limitation of the intermolecular cross-coupling is in most cases the lack of regioselectivity in the coupling reaction when unsymmetrical zirconacyclopropanoids are used [2 a, 3 b, 3e], and the poor coupling in the case of terminal alkynes [3c]. On the other hand, 2-lithioallylamines have been prepared by brominelithium exchange from 2-bromoallylamines [4]. In the present communication we describe the prep aration of ^-propargylam ine-zirconocene com plexes from 2-bromoallylamines and further coup ling with unsaturated compounds followed by iodinolysis. Results and DiscussionTreatment of N-(2-bromoallyl)-N-methylaniline 1 with /erf-butyllithium at -7 8 °C followed by re action with zirconocene methyl chloride at tem peratures ranging between -7 8 and -2 0 °C afReprint requests to Dr. J. Barluenga. r r

Titanium Complexes Stabilized byN-(tert-Hydrocarbyl)anilide Ligation: A Synthetic Investigation

“…Group 4 organometallic molecules are under heavy investigation as catalysts and as stoichiometric reagents for a wide range of transformations including olefin polymerization, reductive coupling, − and hydrogenation catalysis. − While the discovery of well-behaved metallocene-based catalysts for stereospecific polymerization of prochiral olefins has led to a renewed interest in such systems, the search is on for non-cyclopentadienyl ligand systems that may provide catalysts with improved properties. Thus, group 4 organometallic molecules with N- or O-donor ancillary ligands, − or boron-based ligands, − are now under inspection in the hopes that these may provide the next generation of reagents or catalysts.…”

Cross‐Coupling–Elimination Reactions Mediated or Catalyzed by Zirconium Complexes: A Valuable Tool in Organic Synthesis

“…The first reported example of the reaction of an alkynezirconocene complex and heterosubstituted olefins was published in 1995 by Barluenga et al [33] In this reaction the treatment of N-(2-bromoallyl)-N-methylaniline (100) with tert-butyllithium followed by the addition of chloro(methyl)zirconocene and further reaction with butyl vinyl ether or vinyl bromide gives, after treatment with iodine, the 1,3-butadiene 101 (Scheme 20).…”