Applications of the Chiral Auxiliaries DIOZ and TRIOZ for Conjugate Additions and Comparison with Other Auxiliaries

Abstract

A number of N-acryloyl-, N-crotonoyl-, N-(3,3,3-trifluorocrotonoyl)-, N-cinnamoyl-, and N-(3-nitroacryloyl)-4-isopropyl-or -4-phenyl-oxazolidin-2-ones with geminal diphenyl substitution, i.e., 7 -15, have been prepared and used for conjugate additions of organocuprate reagents (Me, i Pr, Ph, 4-MeOPh) in the b-carbonyl ( Table 2) and in the a-carbonyl position (NO 2 -derivative 11 in Scheme 3). The yields and diastereoselectivities are compared with previously tested enoyl-oxazolidinones ( Table 2). Highest diastereoselectivities (> 90%) are always observed with the 4-Ph derivatives (Hruby effect). Nitroacryloyl-oxazolidinones and a corresponding phenylmenthol ester undergo less diastereoselective additions (Scheme 3). A 3-(1-methylethyl)-5,5-diphenyloxazolidin-2-one (DIOZ)-derived Li 2 -enolatenitronate was also tested for a-carbonyl alkylation (Scheme 4). The X-ray crystal structures of three acryloyl-oxazolidinones and of four adducts are described (Tables 1 and 3), and they serve for configurational assignments and description of the stereochemical courses of the additions and alkylation. Possible applications of the nitro compounds for the preparation of b 2 -amino acids are discussed (Scheme 2).

Structure‐Based Evolution of Subtype‐Selective Neurotensin Receptor Ligands

“…Therefore, the two enantiomers of β 2 -homotyrosine described by Sebesta et al 14 have been used, and the two new β 2 -amino acids 4 a and 4 b , with an additional homologation in the side chain, have been synthesized (Scheme 1 ). Preparation of the two β 2 -amino acids 4 a and 4 b was conducted according to the procedure described by Seebach and co-workers, 14 which is based on the use of 4-isopropyl-5,5-diphenyloxazolidin-2-one (DIOZ), 15 a modified Evans oxazolidinone-auxiliary. 16 …”

Iron-Mediated Radical Halo-Nitration of Alkenes

“…In organic synthesis, nitro compounds are valuable synthetic intermediates because these compounds can be easily transformed into amines and ketones . Classical nitration of aromatics and alkenes by electrophilic substitution using nitronium cation (NO 2 + ) is well-known (Scheme , eq 1). − In particular, nitryl chloride (NO 2 Cl) and nitrosyl chloride (NOCl) have been frequently used as a nitro group donor. ,,, However, nitration reactions using these reagents have drawbacks such as difficulty of handling and the limitation of substrates due to toxicity and extreme reactivity. As a method for synthesis of aliphatic nitro compounds, nucleophilic substitution reaction of an alkyl halide with nitrite anion (NO 2 − ) has been used (Scheme , eq 2) .…”

Nitration of Silyl Allenes To Form Functionalized Nitroalkenes

“…One of the most representative nitration methods is based on the addition of nitrogen dioxide with an alkene starting material (Scheme , eq 1) . To generate structurally more elaborate nitro compounds, we envisioned the corresponding nitration of silyl allenes, which so far has not been reported in the literature (eq 2) .…”