Photochemical Mn-Mediated Generation of Azide Radicals for Improvement of Alkene Hydroxyazidation

State-of-the-art strategies for alkene-hydroxyazidation, which yield a mixture of β-azido alcohol and β-azido peroxide, must rely on phosphine reagents to improve the chemoselectivity. To overcome the above problems, we present a photochemical hydroxyazidation of alkenes via Mn-mediated ligand-to-metal charge transfer (LMCT) in O2, which activates N3- to •N3 and incorporates O2 to be used as an oxygen source in the hydroxyazidation products. Broad alkene range and step-economy chemistry for the hydroxyazidation transformation were also demonstrated.

Behaviour of some 1-C-acceptor-substituted glycals under azidohydroxylation conditions

Azidohydroxylation of 1-carbamoyl, 1-methoxycarbonyl and 1-cyano substituted d-lyxo and d-arabino configured O-peracylated glycals was studied and the reaction conditions were optimized. Under these conditions (3 equiv. NaN₃/2 equiv. PIFA/0.3 equiv. TEMPO/50 equiv. H₂O/dry DCM/0 °C/Ar) the expected 3-azido-3-deoxy ulopyranosonic acid derivatives were isolated in good yield with α-d-galacto configuration exclusively from the reaction of the 1-carbamoyl and 1-methoxycarbonyl substituted d-lyxo configured O-peracetylated glycals, while the transformation of the 1-cyano derivative gave a 2,3-vicinal diazide in low yield. The 1-carbamoyl d-arabino configured O-perbenzoylated glycal gave a mixture of α-d-gluco and α-d-manno configured azidohydroxylated products with d-gluco preference. The analogous 1-methoxycarbonyl derivative gave an inseparable product mixture and no transformation was detected with the respective 1-cyano glycal.

Selective Azidooxygenation of Alkenes Enabled by Photo-induced Radical Transfer Using Aryl-λ3-azidoiodane Species

The photolytic radical-induced vicinal azidooxygenation of synthetically important and diverse functionalized substrates including unactivated alkenes is reported. The photoredox-catalyst/additive-free protocol enables intermolecular oxyazidation by simultaneously incorporating two new functionalities; C-O and C-N across the C=C double bond in a selective manner. Mechanistic investigations reveal the intermediacy of the azidyl radical facilitated via the photolysis of λ³-azidoiodane species and cascade proceeding to generate an active carbon-centered radical. The late-stage transformations of azido- and oxy-moieties were amply highlighted by assembling high-value drug analogs and bioactive skeletons.

Regiodivergent and stereoselective hydroxyazidation of alkenes by biocatalytic cascades

Asymmetric functionalization of alkenes allows the direct synthesis of a wide range of chiral compounds. Vicinal hydroxyazidation of alkenes provides a desirable path to 1,2-azidoalcohols; however, existing methods are limited by the control of stereoselectivity and regioselectivity. Herein, we describe a dual-enzyme cascade strategy for regiodivergent and stereoselective hydroxyazidation of alkenes, affording various enantiomerically pure 1,2-azidoalcohols. The biocatalytic cascade process is designed by combining styrene monooxygenase-catalyzed asymmetric epoxidation of alkenes and halohydrin dehalogenase-catalyzed regioselective ring opening of epoxides with azide. Additionally, a one-pot chemo-enzymatic route to chiral β-hydroxytriazoles from alkenes is developed via combining the biocatalytic cascades and Cu-catalyzed azide-alkyne cycloaddition.

Highly Diastereoselective Construction of Carbon- Heteroatom Quaternary Stereogenic Centers in the Synthesis of Analogs of Bioactive Compounds: From Monofluorinated Epoxyalkylphosphonates to α-Fluoro-, β-, or γ-Amino Alcohol Derivatives of Alkylphosphonates

The synthesis of the stable surrogates of an important amino acid (R)-4-amino-3-hydroxybutyric acid (GABOB) such as substituted hydroxy aminophosphonic acids bearing a quaternary stereogenic center is presented. Highly diastereoselective formations of fluorinated spiroepoxy alkylphosphonate or related tertiary carbon-containing oxiranes from β-keto phosphonates possessing methyl, phenyl, or cyclohexenyl substituents, are reported. Stereoselective acid-promoted epoxide opening by bromide or azide followed by reduction/protection afforded tertiary bromides or N-Boc derivatives of β-amino-γ-hydroxy alkylphosphonates in most cases, while the reactions of oxiranes with different amines yielded their β-hydroxy-γ-amino regioisomers. Surprisingly, during the synthesis of amino phosphonic acids, we observe that the acid-induced rearrangement proceeded in a high diastereospecific manner, leading finally to substituted β-hydroxy-γ-aminoalkylphosphonic acids.

Hypervalent iodine(iii)-promoted rapid cascade reaction for the synthesis of unsymmetric azo compounds

A rapid three-component cascade reaction for the synthesis of unsymmetric azo compounds via a radical activation strategy has been reported. Various aryldiazonium salts and unactivated alkenes are well compatible, providing the corresponding products in good to excellent yields. This strategy gives an efficient and practical solution for the synthesis of unsymmetric azo compounds with two C-N bond formation. A free radical pathway mechanism is advised for this transformation.

Visible light photoredox alkylazidation of alkenes with sodium azide and heteroarenium salts: entry to azido-containing 1,4-dihydropyridines

A three-component alkene alkylazidation using sodium azide as the azido resource and heteroarenium salts as functionalized alkyl reagents for producing highly valuable 2-azido-1-(1,4-dihydropyridin-4-yl)-ethanes is described. This reaction allows the incorporation of both an azido group and a 1,4-dihydropyridin-4-yl group across C[double bond, length as m-dash]C bonds to construct two new bonds in a single reaction step, and represents a practical and mechanistically distinct alternative that harnesses an electrophilic heteroarenium ion to accomplish the alkene difunctionalization reaction.

Alkene Syn- and Anti-Oxyamination with Malonoyl Peroxides

Malonoyl peroxide 6 is an effective reagent for the syn- or anti-oxyamination of alkenes. Reaction of 6 and an alkene in the presence of O-tert-butyl-N-tosylcarbamate (R³ = CO₂^tBu) leads to the anti-oxyaminated product in up to 99% yield. Use of O-methyl-N-tosyl carbamate (R³ = CO₂Me) as the nitrogen nucleophile followed by treatment of the product with trifluoroacetic acid leads to the syn-oxyaminated product in up to 77% yield. Mechanisms consistent with the observed selectivities are proposed.

Electronic halocyclization and radical haloazidation of benzene-linked 1,7-dienes for the synthesis of functionalized 3,1-benzoxazines

Electronic halocyclization and radical haloazidation of benzene-linked 1,7-dienes by using TMSN₃ as an azidyl source and NBS as a halogen source has been disclosed in this paper, producing a series of functionalized 3,1-benzoxazines in moderate to good yields.

Azidation in the Difunctionalization of Olefins

Organic azides are key motifs in compounds of relevance to chemical biology, medicinal chemistry and materials science. In addition, they also serve as useful building blocks due to their remarkable reactivity. Therefore, the development of efficient protocols to synthesize these compounds is of great significance. This paper reviews the major applications and development of azidation in difunctionalization of olefins using azide reagents.

I2-mediated regioselective C-3 azidation of indoles

An unprecedented synthesis of novel 3-azido indoles has been developed using I₂ and NaN₃ in high yields and excellent regioselectivity.