A two-phase bromination process using tetraalkylammonium hydroxide for the practical synthesis of α-bromolactones from lactones.

A simple and efficient method for α-brominating lactones that affords α-bromolactones under mild conditions using tetraalkylammonium hydroxide (R4N+OH-) as a base was developed. Lactones are ring-opened with Br2 and a substoichiometric amount of PBr3, leading to good yields of the corresponding α-bromocarboxylic acids. Subsequent intramolecular cyclization over 1 h using a two-phase system (H2O/CHCl3) containing R4N+OH- afforded α-bromo lactones in good yields. This method can be applied at the 10 mmol scale using simple operations. α-Bromo-δ-valerolactone, which is extremely reactive and difficult to isolate, could be isolated and stored in a freezer for about one week using the developed method. Optimizing the solvent for environmentally friendly large-scale syntheses revealed that methyl ethyl ketone (MEK) was as effective. In addition, in situ-generated α-bromo-δ-valerolactone was directly converted into a sulfur-substituted functional lactone without difficulty by reacting it with a sulfur nucleophile in one pot without isolation. This new bromination system is expected to facilitate the industrial use of α-bromolactones as important intermediates.

Identification of dipyrrolone pigments and their precursors formed in the Maillard reaction of carnosine and pentose under weakly acidic conditions.

Colored compounds formed by the Maillard reaction of carnosine with xylose or glucose were investigated in this study. Yellow pigments showing an absorption maximum at 450 nm were found in a heated solution of carnosine with xylose at pH 5.0. These pigments were then isolated and identified as dicarnosyl-dipyrrolones A and B. The generation of dipyrrolones in the absence of lysine suggests that dipyrrolone pigments can be formed by pentose as well as every amino compound such as amino acids, peptides and proteins possessing a free amino group. Analysis of α-dicarbonyls using LC-MS/MS showed that pentosone, 1-deoxypentosone, 3-deoxypentosone (3-DP), and methylglyoxal were predominantly generated via degradation of Amadori compounds. Also, a potential formation pathway of dypyrrolones was established, indicating that an Amadori compound that could form 3-DP is likely to play a role as a main precursor for dipyrrolones.

Sodium Hypochlorite Pentahydrate as a Reagent for the Cleavage of trans-Cyclic Glycols.

Sodium hypochlorite pentahydrate (NaOCl·5H2O) can be used toward the efficient glycol cleavage of trans-cyclic glycols, which are generally resistant to this transformation. Interestingly, the reaction of cis-cyclic glycols with NaOCl·5H2O is slower than that observed for the corresponding trans-isomer. This trans selectivity is in sharp contrast to traditional oxidants used for glycol cleavage. Acyclic glycols can also react efficiently with NaOCl·5H2O to form their corresponding carbonyl compounds in high yield.