Modular Approach to Novel Chiral Aryl-Ferrocenyl Phosphines by Suzuki Cross-Coupling

Abstract

Two novel planar chiral and atropisomeric P,N and P,O aryl-ferrocenyl ligand systems have been developed. The strategy is short and involves a new synthetic approach to aryl-ferrocenyl compounds via a Suzuki cross-coupling procedure. The modular design can easily give access to variety of chiral mono- and bidentate ligands. Two simple derivatives of a novel chiral bidenate P,N ligand belonging to the MOPF family have been synthesized and tested in the enantioselective copper-catalyzed addition of diethyl zinc to an enone and a "difficult" diester. Moderate to excellent yields and enantioselectivities up to 58% were obtained using 1 mol % Cu(OTf)(2) and 1.5 mol % chiral ligand.

The Development of Bidentate P,N Ligands for Asymmetric Catalysis

“…[20] Johannsen and co-workers have recently reported a modular approach to ligands 44 ± 46 and have applied these in copper-catalysed diethylzinc additions. [21] Ligand 46 gave high conversion (95%) and moderate enantioselection (56%) with trans-chalcone as the substrate.…”

Metallocene Sulfoxides as Precursors of Metallocenes with Planar Chirality

“…[55,56,59] The phosphorus group is introduced at the last stage by the sulfoxide-lithium exchange and addition of ClPR 2 or ClPA C H T U N G T R E N N U N G (OPh) 2 . [55,56,59] These phosphines have been named MOPFs (for monophosphine ferrocenes) by Johanssen et al [55] Phosphite 70 (an aryl ferrocenephosphite) was prepared by Woodward et al [58] Carretero et al obtained phosphines 72 (Scheme 15) from ferrocene tert-butyl sulfoxide 4b (Scheme 7) which was functionalized in the ortho-position before the deoxygenation of the sulfinyl group. [54] In Scheme 17 are reported some additional metallocenes prepared by the sulfoxide route with the purpose to be used in asymmetric catalysis.…”

“…[61,62] Aminophosphine 71 is a ligand for a Cu catalyst of the 1,4-addition of Et 2 Zn on chalcone (ee up to 86 %). [59] Phosphite 70 and analogues were used as the ligand of a copper catalyst that gave up to 92 % ee in the conjugated addition of Et 2 Zn on cyclohexenone. [58] Most of the metallocenes with planar chirality developed as ligands for asymmetric catalysis are based on the ferrocene backbone, a new review (published after the completion of this article) details the recent applications of chiral ferrocene ligands in asymmetric synthesis.…”

Phosphines and Related Tervalent Phosphorus Systems

“…Among a considerable range of new monophosphines obtained by trichlorosilane reduction, usually in the final step of the synthesis, are the phosphorus core conjugated triaryl-dendrimer unit (111), 250 a range of triarylphosphines bearing branched fluoroalkyl moieties ('split pony tails'), e.g., (112), 251 and a variety of chiral monophosphines, including the phosphinocarboxylic acid (113), 252 phosphinoaryloxathianes, e.g., (114), 253 a series of axially chiral ortho-aminoarylphosphines, e.g., (115) 254,255 and (116), 256 the axially chiral binaphthylphosphine (117), 257 and the chiral arylferrocenylphosphines (118). 258 Trichlorosilane reduction has also been used in the synthesis of phosphino- [6]-and - [7]-helicenes, e.g., (119), which are also chiral systems, 259,260 and a variety of other chiral diphosphines, including the spiro system (120), 261 the C 2 -symmetric cyclobutane system (121), 262 and the tetraphenylene (122). 263 In addition, many new chiral 2,2 0 -diphosphinobiphenyls have been described, including 'SYNPHOS' (123, X¼CH 2 CH 2 ) 264,265 and 'DIFLUORPHOS' (123, X¼CF 2 ), 266,267 the related system (124), 268 and others involving simple alkoxy substituents in the biphenyl system 269 and bulky aryl groups at phosphorus.…”

“…743 Phosphinidene-nickel 744 and -cobalt 745 complexes have also been trapped with alkynes to form phosphirenes. Other examples of trapping reactions of phosphinidene-metal complexes reported include reactions with alkenes to form phosphiranes, 746 including 1,4-diphosphaspiropentanes 747 and the phospha [7]triangulanes (258), 748 and also with the malonate ion 749 and azulenes. 750 Weak Lewis base adducts of alkyl-and aryl-halides with terminal phosphinidene complexes (formed by thermolysis of azaphosphirene complexes) are involved as intermediates in reactions with benzyl bromide, 2-bromopyridine and bromobenzene, the overall course of the reaction depending on the nature of the organic halide.…”