Catalytic Asymmetric Synthesis of Chiral Allylic Amines. Evaluation of Ferrocenyloxazoline Palladacycle Catalysts and Imidate Motifs

Abstract

Palladium(II) catalysts based on a ferrocenyloxazoline palladacyclic (FOP) scaffold were synthesized and evaluated for the rearrangement of prochiral allylic N-(4-methoxyphenyl)benzimidates. When iodide-bridged dimer FOP precatalysts are activated by reaction with excess silver trifluoroacetate, the allylic rearrangement of both E and Z prochiral primary allylic N-(4-methoxyphenyl)benzimidates takes place at room temperature to give the corresponding chiral allylic N-(4-methoxyphenyl)benzamides in high yield and good ee (typically 81-95%). Several allylic imidate motifs were evaluated also. Because the corresponding enantioenriched allylic amide products can be deprotected in good yield to give enantioenriched allylic amines, allylic N-aryltrifluoroacetimidates were identified as promising substrates.

Chemistry of the highly stable hindered cobalt sandwich compound (η5-Cp)Co(η4-C4Ph4) and its derivatives

“…A useful variant of this transformation involves conversion of allylic trichloro and [204] Overman, after trying out many catalysts, discovered that planar chiral ferrocene based palladacycles (Ferrocenyl oxazoline palladacycles, FOP) activated by silver salts were one of the best catalysts suitable for this rearrangement with yields around 67% and enantiomeric excess of 91% [203,207] (Chart 11). Studies reported in 2003 by Overman, Richards and others indicated that cobalt oxazoline palladacycles (COP) in which the ferrocene unit is replaced by a CpCoC 4 Ph 4 unit (Chart 11) were even better catalysts than the FOP catalysts [205].…”

“…The ferrocenyl oxazoline and cobalt oxazoline palladacycles [203,205,207] Overman-Claisen rearrangement of trichloroacetimidates to trichloroacetamides has been a standard reaction carried out to compare the efficiency of many catalysts especially in terms of Overman, Richards and coworkers fine tuned some of these catalysts for better yield and enantioselectivity and a range of catalysts, basically varying in the additional ligands bound to palladium were reported [204,[208][209][210] [204,[208][209][210] Sutherland reported a tandem aza-Claisen rearrangement and ring closing metathesis for the synthesis of cyclic trichloroacetamides using the COP catalysts [216]. Batey and coworkers reported [3,3] sigmatropic rearrangements of 2-allyloxy pyridines and allyloxy iminodiazaphospholidines using the COP catalysts [217,218].…”

Preparation of ferrocenyl imidazolines using bis(triphenyl)oxodiphosphonium trifluoromethanesulfonate

“…In addition, chiral ferrocenyl imidazolines have also been synthesized by Peters and coworkers [14][15][16][17][18][19][20][21] . They found the planar chiral palladacycles derived from the above chiral ferrocenyl imidazolines were able to catalyze the aza-Claisen rearrangements with up to excellent enantioselectivities [21][22][23][24][25][26][27][28] . Interesting as these chiral ferrocenyl imidazolines, their synthesis somehow is not straightforward.…”

Synthesis, characterization and crystal structures of boron-containing intermediates in the reductive amination of ferrocenecarboxaldehyde to a bis(ferrocenylmethyl) amine

“…The stability, low cost and reversible redox activity of ferrocene have led to widespread applications of ferrocene monomers, oligomers, and polymers, e.g., as catalysts for organic synthesis [1][2][3][4][5][6][7], in conducting polymers [8,9], in photoinduced electron-transfer systems [10], as electrontransfer mediators [11] and as metal scavengers [12]. The stability of ferrocenes in aqueous, aerobic media has made them ideal for applications in biological systems, with ferrocene derivatives of amino acids, carbohydrates, DNA, and hormones being thoroughly investigated [13].…”