Developing Chiral Dibenzazepine-Based S(O)-Alkene Hybrid Ligands for Rh(I) Complexation: Catalysts for the Base-Free Hayashi–Miyaura Reaction

Abstract

A stereodivergent synthesis using inexpensive reagents, i.e., dibenzazepine and glucose-derived t-Bu-sulfinate diastereomers (R S )-6 or (S S )-6, affords respective S(O)-alkene hybrid ligands (S)-7 and (R)-7 on gram scales and in excellent optical purity (ee > 99%). Phenyl substitution of the dibenzoazepine backbone generates planar chirality to give epimerizationresistant (pS,R S )-10 diastereoisomer in high isomeric purity. Furthermore, the crystal structure of widely used sulfinate (R S )-6 is disclosed for the first time since its discovery a quarter of a century ago. Ligands 7 and 10 coordinate Rh(I) in a bidentate fashion through the S atoms and the alkene functions as evidenced by the crystal structures of complexes (R)-11 and (S N ,S S )-12. (R)-11 catalyzes the conjugate addition of arylboronic acids to enones with enantioselectivities of up to 77% ee. The reaction proceeds smoothly also under base-free conditions at 40 °C. The planar chirality in ligand (pS,R S )-10 is shown to override and invert the sense of chiral induction predicted by the configuration of the sulfur donor atom.

Tricyclic Sulfoxide–Alkene Hybrid Ligands for Chiral Rh(I) Complexes: The “Matched” Diastereomer Catalyzes Asymmetric C–C Bond Formations

“…Multi-gram synthesis of 8 and its planar-chiral structure in the crystal (i) PhB(OH) 2 (1 equiv), Pd(PPh 3 ) 4 (5 mol%), DME, reflux, 18h; (ii) HCl, THF, reflux 72h; (iii) AlCl 3 , LiAlH 4 , Et 2 O/THF, reflux, 16h; Crystal structure of 8 (50% displacement ellipsoids, H atoms omitted). Selected distances (Å) and angles (º): C(1)-C(2) 1.3465 (19), C(1)-C(2)-C(3) 128.71 (13), C(2)-C(1)-C (15) 123.68(12), C8-C9-C10 110.97 (11).…”

“…Molecular structures of (S S ,S C )-9 (top) and (S S ,R C )-10 (bottom) in the respective chiral crystals (50% displacement ellipsoids, H atoms are omitted except on C1). Selected distances (Å) and angles (º) for (S S ,S C )-9: S1-O1 1.4983(17), S1-C1 1.894(3), S1-C22 1.856(3), C8-C9 1.353(3), C9-C16 1.499(4), C22-S1-C1 101.82 (11), O1-S1-C1 106.73 (11), O1-S1-C22 105.15 (11), C2-C1-S1 110.63(16), C8-C9-C16 116.6(2), C2-C1-C15 114.0(2); for (S S ,R C )-10: S1-O1 1.5006 (13), S1-C1 1.8714(17), S1-C16 1.8534(17), C8-C9 1.347 (2), C8-C20 1.491 (2), C16-S1-C1 100.32 (8), O1-S1-C1 106.74 (8), O1-S1-C16 106.37 (8), C2-C1-S1 109.64 (11), C9-C8-C20 119.46 (15), C2-C1-C15 111.5 (14). 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 The coordination behavior of (S S ,S C )-9 and (S S ,R C )-10 with Rh(I) was assessed by reacting two equivalents of the respective ligands with [RhCl(coe) 2 ] 2 (coe = cyclooctene) in benzene or toluene solution to yield almost quantitatively dinuclear complexes (R,S)-11 and (R,R)-12 as yellow-orange powders (Scheme 4).…”

“…Submitted to Organometallics 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 (d, J H,H = 6.0 Hz, 1H, ArH), 5.27 (s, 1H, S-CHR 2 ), 1.24 (s, 9H, C(CH 3 ) 3 ) ppm. 13 C NMR (151 MHz, CDCl 3 ): δ 145.5, 144. 2, 137.5, 136.6, 136.0, 135.4, 130.8, 130.7, 129.9, 129.7, 129.6, 129.3, 129.2, 128.5, 128.4, 127.9, 127.8, 127.6, 71.6, 55.7, 23.6 ppm.…”

“…The solid was separated by filtration and dried in vacuo to yield a yellow powder (379 mg, 97% 26H,ArH,major isomer),26H,ArH,minor isomer), 5.16 (s, 2H, S-CHR 2 , minor isomer), 5.08 (s, 2H, S-CHR 2 , major isomer), 1.20 (s, 18H, C(CH 3 ) 3 , minor isomer), 1.04 (s, 18H, C(CH 3 ) 3 , major isomer) ppm. 13 C NMR (400 MHz, CD 2 Cl 2 ): δ 146. 31, 146.18, 139.91, 139.62, 138.91, 136.10, 136.00, 134.35, 131.57, 131.30, 130.87, 129.38, 128.92, 128.12, 127.74, 127.59, 127.34, 127.34, 125.65, 79.83, 78.00, 71.92, 71.45, 68.55, 63.04, 62.00, 26.39, 26.41 ppm.…”

“…Inspired by Knochel's highly effective sulfoxide-alkene 3 11 and Liao's stereoselectivity-switching S(O)-alkenes (both planar-chiral systems), 12 we recently disclosed the planar-chiral sulfonamide 4. 13 Since this ligand proved stereochemically stable only at specific pH values, we were interested in replacing the sulfinamido S-N bond 14 with the more robust sulfoxide S-C bond of the dibenzo-tropylidene analogue (i.e. replacing the N atom with a C-H moiety, see Table 1).…”