Lewis acid-catalysed reactions of 2,2,2-trichloroethyl 6-diazopenicillanate and imines: rearrangements of spiro-6-aziridine- and spiro-6-oxirane-penicillanates. X-Ray crystal structures of (3S,6′S]-2,2,2-trichloroethyl 3-[4-nitrophenyl)-1-phenylspiro[aziridine-2,6′-penicillanate] and (3S,7aR)-2,2,2-trichloroethyl 2,3,5,7a-tetrahydro-7-methoxy-2,2-dimethyl-6-(4-nitrophenyl)-5-oxopyrrolo[2,1-b]thiazole-3-carboxylate

Abstract

Lewis Acid-catalysed Reactions of 2.2.2-Trichloroethyl6-Diazopenicillanate and Imi nes: Rearrangements of Spi ro-6-Azi ridine-and Spi ro-6-oxi ranepen ic i I I a nates. X -Ray C ryst a I St ruct u res of (3S,6'S] -2,2,2-Trichloroeth y/ 3-[ 4-N it rophenyl) -1 -phenylspi ro [aziridi ne-2.6'-penici I lanate] and (3S.7aR) -2,2,2-Tric h loroet hyl2,3,5,7a -Tet ra hyd ro-7-met hoxy-2.2-d imet hyl -6-(4nit rophenyl ) -5oxopyrrolo[2.1 -b]thiazole-3-carboxylate

Catalytic Asymmetric Aziridination with Borate Catalysts Derived from VANOL and VAPOL Ligands: Scope and Mechanistic Studies

“…A single recrystallization (hexanes) of 86 % ee material gave 10 j with 40 % recovery and 96.6 % ee. R f = 0.33 (ethyl acetate/hexanes 1:9); 1 52 (m, 1 H), 1.45 (m, 1 H), 1.25 (t, J = 7 Hz, 3 H), 1.10 (m, 1 H), 1.05 (m, 1 H) A C H T U N G T R E N N U N G (2S,3S)-Ethyl 1-benzhydryl-3-cyclohexylaziridine-2-carboxylate (10 k): [7a] Imine 9 k (277 mg, 1 mmol) was reacted according to the general Procedure F described above with (R)-VANOL as ligand. The only difference was that the reaction was carried out at 0 8C.…”

“…After the addition, the solution was stirred for 40 min and then a vacuum (0.1 mm Hg) was gradually applied to remove the solvent and volatile materials and then the residue was heated at 100 8C under high vacuum for 30 min. The prepared catalyst was dissolved in CDCl 3 and examined by 1 H NMR which indicated that the conversion of VANOL was 100 % (d = 8.43, doublet) and the ratio of the two catalyst species (25/24) is 1:4.8 by integration of the multiplet at d = 8.14 and the doublet at d = 8.04, respectively. The ratio of the two catalyst species (25:24) is 1:5.0 by integration of the multiplet at d = 7.86 and the doublet at d = 7.77, respectively.…”

“…Nonlinear studies with scalemic VANOL and VAPOL reveal an essentially linear relationship between the optical purity of the ligand and the product suggesting that the catalyst incorporates a single molecule of the ligand. Two species are present in the catalyst prepared from BA C H T U N G T R E N N U N G (OPh) 3 and either VANOL or VAPOL as revealed by 1 H NMR studies. Mass spectral analysis of the catalyst mixture suggests that one of the species involves one ligand molecule and one boron atom (B1) and the other involves one ligand and two boron atoms (B2).…”

“…[1][2][3] The mechanism of these reactions (Scheme 1) is distinctively different from those involving copper or rhodium catalysts where a metal carbene or metal carbenoid is involved. [4] The scope of the Lewis acid mediated reactions was not appreciated until the reports by Brookhart and Templeton in 1996 [5] and Jorgensen in 1997.…”

“…Furthermore, the ratio of VANOL derived B2 to B1 catalyst could not be driven past 2:1 even with conditions (Procedure F) that gave a 20:1 selectivity for the VAPOL ligand. The B2 and B1 forms of VANOL were also tentatively assigned by 1 H NMR and high resolution mass spectrum.…”