Vanadium(V)-Catalyzed Oxidative Bromination of Acid Labile Alkenols and Alkenes in Alkyl Carbonates

Abstract

Molecular bromine is formed from bromide and tert-butyl hydroperoxide under mild and neutral conditions. The oxidation is catalyzed by vanadium(V)-complexes and requires bromide- and proton- aliquots that are slowly released from a 3-bromopropionic acid-bromide buffer in solutions of alkyl carbonates. In such an environment, bromocyclization of acid labile alkenols occurs without hydrolytically cleaving acetal- or ester-protecting groups. 4-Pentenols having methyl- and/or phenyl-groups attached to the terminal carbon atom of the alkenol double bond undergo 6-endo-selective ring closures if subjected to oxidative bromination and provide bromotetrahydropyrans in synthetically useful yields. Application of the new procedure affords a hexasubstituted tetrahydropyran-building block en route to synthesis of the marine natural product aplysiapyranoid A.

Chemoenzymatic Production of Enantiocomplementary 2‐Substituted 3‐Hydroxycarboxylic Acids from l‐α‐Amino Acids

“…The product 5 a was obtained as a solid (30 mg, 51%). The NMR spectra of this product agreed with those reported in the literature [18] . 1 H NMR (CDCl 3 , 400 MHz): δ =3.60 (s, 2H) 1.23 (s, 6H).…”

Photocatalytic Selective Bromination of Electron-Rich Aromatic Compounds Using Microporous Organic Polymers with Visible Light

“…Apart from the bromination reagent perspective, another consideration for the bromination reaction of aromatic compounds is the catalyst design. In the past, noble-metal-based catalysts such as indium, gold, ruthenium, and palladium, , and non-noble metal-containing catalysts such as copper, iron, and vanadium have been used for various bromination reactions. However, there are still some intrinsic drawbacks associated with these metal-based catalysts, for instance, the high cost and toxicity, as well as the limited availability in nature.…”

Thymol Bromination – A Comparison between Enzymatic and Chemical Catalysis

“…[4] A wide variety of vanadium complexes have been synthesized and used as functional models for V-haloperoxidases in order to have a better understanding of the mechanism of action of such enzymes, and these complexes are effective catalyst precursors in various oxidation reactions such as epoxidation of alkenes, oxidation of sulfides, alkanes, arenes and alcohols, as well as in oxidative bromination reactions in the presence of hydrogen peroxide [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25] or alkyl hydroperoxides. [26] Inspired by the mechanism of action of V Br PO, a biphasic procedure for bromination reactions was proposed in 1994. [27] According to this procedure, in order to mimic the hydrophobic and hydrophilic regions of the enzyme, a double-phase system is required (Scheme 2).…”