Chiral Phosphinoferrocenyl‐Calixarenes

Abstract

The Mitsunobu alkylation of 4‐tert‐butylcalix[4]arene with (S)‐(2‐diphenylthiophosphinoferrocenyl)methanol followed by desulfuration of the thiophosphine unit using tris(dimethylamino)phosphine afforded enantiomerically pure calixarene mono‐ and di(ferrocenylphosphine) ligands in high yields. The calixarene mono(ferrocenylphosphine) ligands exhibited good catalytic activity but low atropoenantioselectivity when used in the asymmetric Suzuki–Miyaura coupling reaction of 1‐naphthaleneboronic acid and 1‐bromo‐2‐methylnaphthalene. However, the di(ferrocenylphosphine) ligand displayed both good catalytic activity and enantioselectivity (ee values up to 86 %) when employed in the asymmetric Tsuji–Trost allylic alkylation of 1,3‐diphenylprop‐2‐enyl acetate with dimethyl malonate.

Recent applications of chiral calixarenes in asymmetric catalysis

“…Manoury et al described the synthesis of ferrocene-bearing enantiomerically pure calixarenes and their catalytic performances in the asymmetric Suzuki–Miyaura coupling and Tsuji–Trost allylic alkylation reactions ( Scheme 7 ) [ 42 ]. Calix[4]arene mono and dithiophosphines 24 – 26 were efficiently synthesized from p-tert -butylcalix[4]arene by a one pot Mitsunobu alkylation using enantiomerically pure ( S )-(2-diphenylthiophosphinoferrocenyl)methanol.…”

(Planar‐Chiral) Ferrocenylmethanols: From Anionic Homo Phospho‐Fries Rearrangements to α‐Ferrocenyl Carbenium Ions

“…Nevertheless, the use of this 1‐PPh 2 ‐2‐OMe ferrocene as a ligand for C , C cross‐coupling catalysis did not result in a detectable ee in the formed biaryls, due to the geometry of the ferrocenyl C 5 H 3 ring and the low steric demand of the hemi‐labile methoxy group. Replacement of the methyl by an aryl group could therefore enhance the chirality transfer within the C , C cross‐coupling protocol, due to steric reasons and attractive dispersion interactions , , . Attempts to adopt this strategy on 1,2‐P,O ferrocenes were successful by applying nucleophilic aromatic substitution reactions by using electron deficient arenes , .…”

“…In addition, 1-PPh 2 -2-CH 2 OR ferrocenes, where an additional methylene group is present between the ferrocenyl backbone and the oxygen donor atom, were prepared. [11,14] The usage of this type of sandwich compounds as ligands within Suzuki-Miyaura C,C cross-coupling reactions gave the respective biaryls with an ee of up to 37 %, most likely due to the planar as well as the C-central chirality. The angle between the P-and Odonor atoms also seems to play a decisive role ( Figure 1).…”

“…and solid(11) after removal of all volatiles in vacuo. Compound 11 was obtained as a mixture of the tautomeric forms 11a and 11b.…”

Crystal structure of (2-acetylferrocen-1-yl)boronic acid

“…The synthesis of 1,2-functionalized ferrocenes is a striking topic in ferrocene chemistry (Schaarschmidt & Lang, 2013;Korb et al, 2014a) and is mostly realized via ortho-directed metalation and subsequent reaction with electrophiles (Schaarschmidt & Lang, 2013) or intramolecular rearrangement (Werner & Butenschö n, 2013;Korb et al, 2017). The resulting ferrocenes are predominantly used as ligands in C,C cross-coupling catalysis (Schaarschmidt et al, 2014;Jensen & Johannsen, 2003;Vinci et al, 2009;Debono et al, 2010;Karpus et al, 2016), but also the introduction of ferrocenyl substituents by catalytic conversions is of rising interest (Hildebrandt et al, 2011a,b;Speck et al, 2015;Korb et al, 2014b). The introduction of electronically and sterically modified substrates requires the synthesis of the respective ferrocenes that bear groups suitable for oxidative additions or transmetalation reactions (Lehrich et al, 2015;Speck et al, 2014).…”