Chiral Dirhodium(II) Carboxamidates for Asymmetric Cyclopropanation and Carbon–Hydrogen Insertion Reactions

Abstract

In 1989-1990 three groups published initial results relating to the development of dirhodium(II) catalysts for asymmetric transformations of diazo compounds [1][2][3]. Two focused on amino acid carboxylate ligands [1,2], and one of them fortuitously found that prolinate ligands had unusual selectivity in reactions of diazoacetates and related substrates [2], even though the ligand's chiral centers lie far from the axial sites of dirhodium(II), which is where the carbene intermediate is formed. This discovery has led to very significant undertakings by Davies, particularly with aryl-and vinyldiazoacetates [4-8], but they have already been described in Chapter 14.On the basis of reports by Bear and co-workers [10-12] and the discovery that carboxamidate ligands could be introduced onto dirhodium(II) by semi-automated methods [13], Doyle and co-workers began their development of carboxamidate ligands for dirhodium with oxazolidinones (for example, 1 and 2), but with limited success in achieving high enantiocontrol [3]. Only when a carboxylate attachment, as in pyrrolidinone 3, rather than an isopropyl or benzyl group, as in 1 or 2, was placed in proximity to the reaction center, could high enantiocontrol be achieved [14]. The key developments here were: 1) the methodology for the semi-automated synthesis of dirhodium(II) carboxamidates by trapping acetic acid with sodium carbonate in a Soxhlet extraction apparatus (Eq. 1) [15]; and 2) the discovery of the high selectivity enhancement afforded by the carboxylate attachment [16]. Scheme 15.6 (cont.) Scheme 15.7 Synthesis of 2-deoxyxylolactone. 93 : 7

Chiral Dirhodium(II) Carboxylates and Carboxamidates as Effective Chemzymes in Asymmetric Synthesis of Three‐Membered Carbocycles

“…As a consequence, these complexes can only obtain C 2 symmetry due to this intrinsic ligand binding propensity. 100,101 The further development of this (2,2)-cis geometry strategy was the synthesis of imidazolidinone carboxylate catalysts with chiral N-acyl attachments (76-90, Fig. 16) and Rh 2 (4S-MEOX) 4 (61, Fig.…”

“…19). 100,101 The further development of this (2,2)-cis geometry strategy was the synthesis of imidazolidinone carboxylate catalysts with chiral N-acyl attachments (76-90, Fig. 17).…”

Chiral Dirhodium Catalysts: A New Era for Asymmetric Catalysis

“…Ideally, a practical asymmetric catalyst is inexpensive and readily available in both enantiopure forms whilst providing high yields and enantioselectivities for a broad range of substrates in different reactions. A large number of complexes have been synthesized and many of these complexes have been studied and used in catalysis [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18]. The catalysis by dirhodium paddlewheel complexes has been an area of immense interest and extensive study over the past three decades -not only because most of the catalysts are highly stable to heat, moisture and ambient atmosphere but also for the asymmetric induction in the ylide generation [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19].…”

Photosensitized O 2 enables intermolecular alkene cyclopropanation by active methylene compounds

“…Among the limited methods available for intermolecular cyclopropanation (8), the most preferred and reliable is carbene insertion into alkenes (9)(10)(11). This method is profoundly dependent on reactive carbene and metal-carbenoid intermediates [[M]=CR 2 ], in particular the donor-acceptor Rh-carbenoids (9,10,12) derived from highly energetic diazoalkanes, which require stringent precautions for handling (13,14).…”