Recent resurgence toward the oxidation of heteroatoms using dimethyldioxirane as an exquisite oxidant

Dioxiranes: A Half-Century Journey

Dioxiranes are multi-tasking reagents inheriting mild and selective oxygen transfer attributes. These oxidants are accessed from the reaction of ketones with an oxidant and are employed stoichiometrically or catalytically (in...

Concise Modular Synthesis and NMR Structural Determination of Gallium Mycobactin T

A modular synthesis of mycobactin T and its N-acetyl analogue is reported in a route that facilitates permutation of the lipid tails. A key feature is the generation of N(α)-Cbz-N(ε)-benzyloxy-N(ε)-Boc-lysine (A4) with methyl(trifluoromethyl)dioxirane in 59% yield. Selective hydroxamate N-acylation was achieved with acyl fluorides, enabling installation of lipids tails in the final step. O-Benzyl-dehydrocobactin T (B4) was prepared by modifying a known five-step sequence with an overall yield of 49%. 2-Hydroxyphenyl-4-carboxyloxazoline (C3) was prepared from 2-hydroxybenzoic acid and l-serine methyl ester in three steps with an overall yield of 55%. Ester coupling of A4 and B4 with EDCI afforded MbI-1 in 73% yield. Catalytic hydrogenation with Pd/BaSO₄ and 50 psi of H₂ simultaneously effected alkene reduction and debenzylation to afford MbI-2 in 96% yield. Fragment C3 was converted into acyl fluoride C4, which coupled with MbI-2 to afford MbI-3 in 51% yield. Finally, Boc-removal with HCl/EtOAc and treatment of the resultant hydroxylamine with stearyl fluoride furnished mycobactin T in 65% yield. Overall, the yield is 4% over 14 steps. The gallium mycobactin T-N-acetyl derivative (GaMbT-NAc) structure was determined by ¹H NMR. The structure shows an octahedral Ga and two internal hydrogen bonds between peptidic N-Hs and two of the oxygen atoms coordinating Ga.

Selective and metal-free epoxidation of terminal alkenes by heterogeneous polydioxirane in mild conditions

Polydioxirane (PDOX) was prepared by the treatment of polysalicylaldehyde with Oxone and was found as a selective, highly efficient and heterogeneous reagent for epoxidation of alkenes which can be successfully isolated. This work also introduced a simpler, safer and milder way for epoxidation of alkenes with dioxirane groups than before. PDOX can be simply recovered from the reaction mixture by plain filtration and reused for eight runs without significant reactivity loss.

Tandem Oxidative α-Hydroxylation/β-Acetalization Reaction of β-Ketoamides and Its Applications

A tandem oxidative α-hydroxylation/β-acetalization reaction of β-ketoamides was developed in the presence of PIDA and NaOH. This reaction proceeded at 25 °C in the absence of a metal catalyst to provide 2-hydroxy-3,3-dimethoxy-N-substituted butanamides in good to excellent yields from readily available starting materials. The application of this chemistry to the construction of α-hydroxy-β-ketoamides and quinolinones was also described.