Control of stereochemistry in free radical reactions with oxazolidine auxiliaries

Diastereoselective Reactions of the Tiglic Acid Functionality Mediated by Oxazolidine Chiral Auxiliaries: A Mechanistic Comparison of DMD andm‐CPBA Epoxidations versus Singlet Oxygen and PTAD Ene Reactions

“…[1] Unfortunately, the presence of a Lewis acid, required for metal chelation, is not compatible with a large number of common oxidants. In the 1990s, Porter and Kanemasa reported the induction of effective diastereochemical control by chiral 2,2-dimethyloxazolidines, in radical additions, [2] nitrile oxide cycloadditions, [3] and conjugate additions of organocuprates [4] to α,β-unsaturated amides. The efficacy of these auxiliaries originates from the conformational alignment of the amide linkage and the shielding of one of the faces of the CC double bond by the proximate substituent at the C-4 position of the oxazolidine ring, [3b] with the steric hindrance imposed by the two methyl groups at the C-2 position of the oxazolidine ring, which forces the amide frag-ment predominantly to occupy the syn/s-cis conformation A (Figure 1).…”

Asymmetric Iodolactamization Induced by Chiral Oxazolidine Auxiliary

“…To (4 S )-4-((2 R )-2-butyl)-2,2-dimethyloxazolidine (1.57 g, 10 mmol) in dry dichloromethane (30 mL) was added the above isocyanate (1.53 g, 10 mmol) in dry dichloromethane (10 mL), and the resulting solution was stirred for 4 h at room temperature. After removal of the solvent, the crude product was purified by column chromatography on silica gel with hexane−acetone (20:1) as the eluent to give the pure 1e as a colorless oil: yield 2.52 g (85%); [α] 25 D = +24.7 ( c 1.00, CH 3 COCH 3 ); 1 H NMR (300 MHz, CDCl 3 ) δ 0.76−0.83 (6H, m), 0.90−1.05 (1H, m), 1.14 (6H, s), 1.21−1.33 (1H, m), 1.49 (3H, s), 1.59 (3H, s), 1.62−1.71 (1H, m), 2.18−2.32 (2H, m), 3.76−3.80 (2H, m), 3.89−3.95 (1H, m), 5.00−5.05 (2H, m), 5.63−5.75 (1H, m), 8.50 (1H, br); 13 C NMR (CDCl 3 ) δ 21.6, 23.1, 23.6, 24.5, 24.6, 25.6, 26.7, 42.6, 43.0, 44.2, 56.4, 67.1, 95.0, 118.6, 133.5, 150.1, 176.3; EIMS m / z (rel intensity) 295 (M + − CH 3 , 4), 252 (7), 237 (6), 210 (21), 169 (10), 142 (100), 100 (24), 83 (65).…”

“…To (4S)-4-((2R)-2-butyl)-2,2-dimethyloxazolidine 19 (1.57 g, 10 mmol) in dry dichloromethane (30 mL) was added the above isocyanate (1.53 g, 10 mmol) in dry dichloromethane (10 mL), and the resulting solution was stirred for 4 h at room temperature. After removal of the solvent, the crude product was purified by column chromatography on silica gel with hexane-acetone (20:1) as the eluent to give the pure 1e as a colorless oil: yield 2.52 g (85%); [R] 25 D ) +24.…”

Radical and Radical–Ionic Multicomponent Processes

“…[26] We will therefore focus on two representative examples, depicted in Scheme 10, that illustrate stereocontrolled versions of 3-CR carboallylation. Diastereoselective approaches relied on the use of chiral sultams, [27] oxazolidines, [28] and oxazolidinones [29] auxiliaries.…”