Chiral Oxo- and Oxy-Functionalized Diphosphane Ligands Derived from Camphor for Rhodium(I)-Catalyzed Enantioselective Hydrogenation

Abstract

The synthesis of two series of diastereomeric oxo-and oxysubstituted diphosphanes 7a−9a and 7b−9b, as well as an analogous nonfunctionalized diphosphane 17, was performed starting from (R)-camphor. The new diphosphanes were used as ligands in the enantioselective rhodium(I)-catalyzed hydrogenation of functionalized olefins − α-and β-dehydroamino acids and their esters − in order to elucidate the [a] effect of the oxo-and oxy-functional groups. The enantioselectivities, ranging from 2−90% ee, and the rates were strongly dependent on the type and relative position of the oxo or oxy substituent in the catalyst. Possible explanations for the effects are given.

Phosphines and Related Tervalent Phosphorus Systems

“…Included among these are aminomethylphosphine derivatives of adenine, 412 the new unsymmetrical phosphine Ph 2 PCH 2 NHC 6 H 4 PPh 2 , 413 a polymer-bound (N-phosphinoethyl)-aminomethylphosphine, 414 and water-soluble aminomethyl(ferrocenylmethyl)-phosphines. 415 Bis(phosphinomethyl)amino systems have also been described, e.g., (166), 416 the amphiphilic and water-soluble systems (167), 417 and a bis(aminomethylphosphine) derived from 3,4-diaminotoluene. 418 The related reactions of bis(hydroxymethyl)organophosphines with primary amines have led to the isolation of new cyclic-and macrocyclic-aminomethylphosphines, e.g., (168).…”

“…Various chiral oxo-and oxy-functional diphosphines, e.g., (83), have been prepared from the camphor system. 165,166 Chiral C 2 -symmetric 1,4-dioxanyldiphosphines, e.g., (84), have been prepared from tartrate esters. 167 Routes to a number of P,P,N-donor systems have been developed, including a trans-chelating 1,5-bis(di-t-butylphosphino)-2-(S)-dimethylaminopentane, 168 2,2 0 -bis(diphenylphosphino)diphenylamine, 169 and a series of tripod ligands (85) involving phosphine and dialkylamine or N-pyrazolyl donors.…”

Synthesis of Functionalized Chiral Imidazole Derivatives Based on a Bornane Skeleton Bearing a Sterically Crowded Spirocyclic Substituent at the C-3 Position

“…Alternatively, conversion of 3a-b into the corresponding 10-iodo derivatives 4a-b was efficiently carried out in high yields by treating with sodium iodide (NaI, 3.0 mol amt.) in N,N-dimethylformamide (DMF) according to the report of Komarov et al 30 Therefore, 10-iodobornane-2-thiones ( 4a-b ) were easily prepared through a two-step conversion from the starting thiones 2 , and the results urged us on the further functionalization of the bornane skeletons toward chiral imidazolium salts by using S N 2-type reactions to the iodine functionality of the C-10 position of the bornane skeleton with imidazole. Preparative methods for 4a-b through the reaction of 3a-b with sodium iodide are summarized in Scheme 2.…”

Synthesis and Structure Determination of 8- and 9-iodocamphorquinone Bis(ethylene ketal)

“…Before attempting to introduce an intrinsically nucleophilic phosphine donor into the 8-iodo diketone 9, the carbonyl groups were protected by acid-catalysed ketalisation following a procedure described by Komarov and co-workers. 5 Spectroscopic analysis of the crude material recovered after the reaction indicated the presence of a mixture of compounds, chromatographic separation of which afforded five different ketal products, viz., the 8-iodo monoketals 12 and 13, the known diketal 14 6 and a pair of isomers. Both isomers exhibited spectroscopic properties consistent with the desired 8-iodocamphorquinone bis(ethylene ketal) 10.…”