Enecarbamates as Selective Substrates in Oxidations:  Chiral-Auxiliary-Controlled Mode Selectivity and Diastereoselectivity in the [2+2] Cycloaddition and Ene Reaction of Singlet Oxygen and in the Epoxidation by DMD and mCPBA

Abstract

The stereochemical course of the oxidation of chiral oxazolidinone-substituted enecarbamates has been studied for singlet oxygen ((1)O(2)), dimethyldioxirane (DMD), and m-chloroperbenzoic acid (mCPBA) by examining of the special structural and stereoelectronic features of the enecarbamates. Valuable mechanistic insight into these selective oxidations is gained. Whereas the R(1) substituent on the chiral auxiliary is responsible for the steric shielding of the double bond and determines the sense of the pi-facial diastereoselectivity, structural characteristic such as the Z/E configuration and the nature of the R(2) group on the double bond are responsible for the extent of the diastereoselectivity. Stereoelectronic steering by the vinylic nitrogen functionality controls the mode selectivity (ene reaction vs [2+2] cycloaddition) in the case of (1)O(2).

Disulfide‐Catalyzed Visible‐Light‐Mediated Oxidative Cleavage of C=C Bonds and Evidence of an Olefin–Disulfide Charge‐Transfer Complex

“…Like in other radical-mediated OCO methods, we also believed that the key intermediate was the dioxetane (6), which was formed from intermediate 5 by the abstraction [26] and substitution of the thiyl radical. Although dioxetane 6 could not be directly observed since it spontaneously decomposed upon formation [6,7] to give product 2a, several observations were informative to confirm the proposed pathway: 1) The tertiary radical (3) from the thiyl addition underwent α-hydrogen abstraction to give trace amount of compound 4, which was observed by GC-MS; 2) When the reaction was performed in the presence of methionine (1 equiv) and water as the trapping reagents for dioxetane, [27] the formation of diol 8 was detected.…”

Direct CH Functionalization of Enamides and Enecarbamates by Using Visible‐Light Photoredox Catalysis

“…[5] Furthermore, as electron-deficient counterparts of enamines, enamides can also be used as nucleophiles to undergo many important transformations. [6] Common strategies used to prepare enamides are based on C À N bond formation, including the condensation of carbonyl compounds with amides [7] or Ullmann-type coupling between vinyl halides and amides. [8] These reported synthetic methods usually require harsh conditions or lead to mixture of Z/E isomers in parallel.…”

A Practical and Effective Ruthenium Trichloride‐Based Protocol for the Regio‐ and Stereoselective Catalytic Hydroamidation of Terminal Alkynes

“…Systematic investigations revealed that a base, for example, potassium carbonate or hydroxide, is essential, whereas the alcohol can be replaced by water (entries [5][6][7][8][9]. This goes along with reports in the literature that phosphines themselves can act as reducing agents for transition metals, a process assisted by water.…”

“…They promise to be valuable alternatives to traditional syntheses, for example, from carbonyl compounds and amides [6] or from hydroxylamines and carboxylic anhydrides, [7] that usually require harsh conditions and give (E/Z)-mixtures, and to metal-catalyzed coupling reactions of amides with vinyl halides, pseudohalides [8] or ethers, [9] which suffer from limited substrate availability.…”