Silver (I)-promoted asymmetric halohydrin reaction of chiral N-enoyl-2-oxazolidinones: scope and limitations

Highly Regio- and Stereoselective Asymmetric Bromoazidation of Chiral α,β-Unsaturated Carboxylic Acid Derivatives: Scope and Limitations

“…Steric effect along with electronic effect might be responsible for substrates 5d and 5e not undergoing the bromoazidation reaction. Stereochemistry of the bromoazides 6 and 7 were assigned by analogy with our earlier work 13a2 Yb(OTf) 3 -Catalyzed Bromoazidation of (2 R )- N -Enoylbornanesultams 5 entrysubstrateAr t (h) T (°C)dr a ( 6:7 )yield b (%) 1 5a C 6 H 5 24 rt NR NR 2 5a C 6 H 5 4 45 70:30 86 3 5b 4-MeOC 6 H 4 2 rt 86:14 85 4 5b 4-MeOC 6 H 4 4 −20 60:40 87 5 5c 3,4-MeOC 6 H 3 1 rt 89:11 88 6 5c 3,4-MeOC 6 H 3 2 −20 65:35 84 7 5d 2-ClC 6 H 4 24 45 NR NR 8 5e 2-NO 2 C 6 H 4 24 45 NR NR 9 5f 4-ClC 6 H 4 36 45 75:25 85 c 10 5g 4-NO 2 C 6 H 4 36 45 73:27 89 d a Determined by HPLC.…”

“…A current interest in our laboratory is to develop asymmetric 1,2-halofunctionalization of alkenes, especially α,β-unsaturated carbonyl compounds . A reliable possibility for exerting stereochemical control in the stereogenic centers is the use of the chiral auxiliary methodology.…”

“…A reliable possibility for exerting stereochemical control in the stereogenic centers is the use of the chiral auxiliary methodology. Recently we have found that Lewis acid activates NBS to facilitate the formation of bromonium ion intermediate from alkenes 13a. Accordingly, we anticipated that a suitable Lewis acid might catalyze the bromoazidation of chiral α,β-unsaturated carboxylic acid derivatives containing a suitable chiral auxiliary with NBS and TMSN 3 .…”

Current Methods for Asymmetric Halogenation of Olefins

“…The use of chiral auxiliaries for asymmetric introduction of halogen atoms onto olefins has only been explored in a limited fashion, using Oppolzers sultam, [9] oxazolidines [10] and oxazolidinones, [11] for example. Diastereomeric ratios are typically poor (< 4:1); however, the products should be readily separable and should provide a way to generate halogenated building blocks in enantiomerically pure form, after auxiliary removal.…”

OP14.12: Independent and combined contribution of cardiovascular Doppler parameters to short‐term prediction of mortality in severe IUGR

“…The use of chiral auxiliaries for asymmetric introduction of halogen atoms onto olefins has only been explored in a limited fashion, using Oppolzer’s sultam,9 oxazolidines10 and oxazolidinones,11 for example. Diastereomeric ratios are typically poor (<4:1); however, the products should be readily separable and should provide a way to generate halogenated building blocks in enantiomerically pure form, after auxiliary removal.…”