An overview of the applications of chiral phosphoric acid organocatalysts in enantioselective additions to CO and CN bonds

Abstract

Chiral phosphoric acids (CPAs) have been used as efficient organocatalysts since the first examples were reported 18 years ago by Akiyama and Terada. Although they were originally developed for enantioselective...

Thermodynamic evaluations of the acceptorless dehydrogenation and hydrogenation of pre-aromatic and aromatic N-heterocycles in acetonitrile

“…In practice, 27H 2 (HEH 2 ), [38][39][40] 67H 2 , 34,35 been extensively researched in hydrogenating various unsaturated compounds, including aldehydes ketones, alkenes, imines, and heterocycles; [36][37][38][39][40][41][42] (2) in contrast, since Y IV were general imines without aromatic structures, all the DG H 2 A (Y IV ) values (−18.3 to −10.3 kcal mol −1 ) were all greater than the DG H 2 R (H 2 ) values (0 kcal mol −1 ), meaning that H 2 could hydrogenate the related general imines (Y IV ) in organic synthesis under suitable catalytic conditions, which has been proved by many published studies in the literature. [43][44][45][46][47] Similarly, HCO 2 H (DG H 2 R (HCO 2 H) = −5.9 kcal mol −1 ), 28 78H 2 (DG H 2 R (78H 2 ) = 0.9 kcal mol −1 ), 36,37 67H 2 (DG H 2 R (67H 2 ) = 3.6 kcal mol −1 ), 34,35 and HEH 2 (DG H 2 R (HEH 2 ) = 7.3 kcal mol −1 ) 38-40 could be applied to hydrogenate Y IV to prepare general amines Y IV H 2 in organic synthesis from a thermodynamics viewpoint.…”

“…It is well known that H 2 is the greenest hydrogenation reagent with 100% atomic economy. [43][44][45][46][47] Besides H 2 , the organic hydrogen molecule reductants, most of which are pre-aromatic N-heterocyclics (such as 27H 2 , 67H 2 , 73H 2 , 74H 2 , and 78H 2 ), [36][37][38][39][40][41][42] are irreplaceable hydrogen carriers in hydrogenation reactions. Zhou et al developed dual hydrogenation strategies and utilized catalytic amounts of Hantzsch ester (HEH 2 or 27H 2 ) 49 and dihydrophenanthridines (67H 2 ) 50 as hydrogen reductants to asymmetrically reduce imines by using H 2 as a real reductant for regeneration of the oxidated Hantzsch esters (HE or 27) under a catalyst of metal complexes (Scheme 7).…”

An update on chiral phosphoric acid organocatalyzed stereoselective reactions

“…7,[41][42][43][44][45] For readers interested in a more specific review article on CO and CN additions, a study by Vicario, Maestro, and co-workers has been recently published. 46 This section covers a range of addition reactions, from the simple inclusion of a hydrogen atom to the tandem reaction of three compounds.…”

Accessing unnatural α-amino acids with tetrasubstituted stereogenic centersviacatalytic enantioselective reactions of ketimine-type α-iminoesters/α-iminoamides

“…6,102 Meanwhile, chiral phosphoric acids (CPAs), which contain Brønsted-acidic sites and Brønsted-basic sites within the same molecule, have been used to catalyze a variety of enantioselective reactions. 103 In 2011, Piersanti and co-workers reported the first organocatalytic enantioselective aza-FC alkylation reaction of indole with generated ketimine 1n derived from methyl a-acetamidoacrylates (Scheme 64A). 104 Among applicable substrates, only one ketimine (i.e., 1n) appears to have been used in this reaction, with chiral ATAA 160 obtained with 66% ee.…”