Negative allosteric modulators of NMDA receptors with GluN2B subunit: synthesis of β-aminoalcohols by epoxide opening and subsequent rearrangement

In order to obtain novel antagonists of GluN2B subunit containing NMDA receptors, aryloxiranes were opened with benzylpiperidines. Phenyloxiranes 6 and (indazolyl)oxirane 15 were opened regioselectively at the position bearing the aryl moiety. Reaction of the resulting β-aminoalcohols 7 and 16 with carboxylic acids under Mitsunobu conditions (DIAD, PPh3) led to rearrangement and after ester hydrolysis to the regioisomeric β-aminoalcohols 9 and 18. This strategy allows the synthesis of amino-ifenprodil 12 as well using phthalimide in the Mitsunobu reaction. Unexpectedly, the isomeric (indazolyl)oxirane 21 reacted with benzylpiperidines to afford both regioisomeric β-aminoalcohols 22 and 23. In radioligand receptor binding studies, the indazolyl derivative 18a, which can be regarded as indazole bioisostere of ifenprodil, showed high GluN2B affinity (Ki = 31 nM). Replacement of the benzylic OH moiety of ifenprodil by the NH2 moiety in amino-ifenprodil 12 also resulted in low nanomolar GluN2B affinity (Ki = 72 nM). In TEVC experiments, 18a inhibited the ion flux to the same extent as ifenprodil proving that the phenol of ifenprodil can be replaced bioisosterically by an indazole ring maintaining affinity and inhibitory activity. Whereas 10-fold selectivity was found for the ifenprodil binding site over σ1 receptors, only low preference for the GluN2B receptor over σ2 receptors was detected. The log D7.4 value of 18a (log D7.4 = 2.08) indicates promising bioavailability.

Enantio- and Z-selective synthesis of functionalized alkenes bearing tertiary allylic stereogenic center

Olefins are ubiquitous in biologically active molecules and frequently used as building blocks in chemical transformations. However, although many strategies exist for the synthesis of stereodefined E-olefines, their thermodynamically less stable Z counterparts are substantially more demanding, while access to those bearing an allylic stereocenter with an adjacent reactive functionality remains unsolved altogether. Even the classic Wittig reaction, arguably the most versatile and widely used approach to construct Z-alkenes, falls short for the synthesis of these particularly challenging yet highly useful structural motives. Here, we report a general methodology for Z-selective synthesis of functionalized chiral alkenes that establishes readily available alkene-derived phosphines as an alternative to alkylating reagents in Wittig olefination, thus offering previously unidentified retrosynthetic disconnections for the formation of functionalized disubstituted alkenes. We demonstrate the potential of this method by structural diversification of several bioactive molecules.

Radical Perfluoroalkylation Enabled by a Catalytically Generated Halogen Bonding Complex and Visible Light Irradiation

Exploiting charge-transfer complexes in visible light-promoted single-electron redox reactions is a promising route for opening novel synthetic pathways, and catalytic approaches to complex formation are critical for facilitating this chemistry. This report describes the use of a substituted hydroquinone catalyst to promote radical perfluoroalkylation reactions. Mechanistic studies indicate that the reaction is initiated through formation of a visible light-absorbing halogen bonding complex between the hydroquinone catalyst and the perfluoroalkyl halide radical precursor.

Tracking down the brominated single electron oxidants in recent organic red-ox transformations: photolysis and photocatalysis

A wide range of organic and inorganic brominated compounds including molecular bromine have been extensively used as oxidants in many organic photo-redox transformations in recent years, an area of ever growing interest because of greener and milder approaches. The oxidation power of these compounds is utilized through both mechanistic pathways (by hydrogen atom transfer or HAT in the absence of a photocatalyst and a combination of single electron transfer or SET and/or HAT in the presence of a photocatalyst). Not only as terminal oxidants for regeneration of photocatalysts, but brominated reactants have also contributed to the oxidation of the reaction intermediate(s) to carry on the radical chain process in several reactions. Here in this review mainly the non-brominative oxidative product formations are discussed, carried out since the last two decades, skipping the instances where they acted as terminal oxidants only to regenerate photocatalysts. The reactions are used to generate natural products, pharmaceuticals and beyond.

Visible light-promoted ring-opening functionalization of three-membered carbo- and heterocycles

In this tutorial review, synthetic and mechanistic aspects of visible light-promoted ring-opening functionalization of three-membered carbo- and heterocycles are highlighted.

Visible-Light Induced Direct Synthesis of Polysubstituted Furans from Cyclopropyl Ketones

In this article, a photoredox protocol for the synthesis of furans via oxidative coupling of olefin generated in situ from cyclopropyl ketones with ketonic oxygen atom is presented. Moreover, bromination of furans in the presence of overstoichiometric oxidant has been achieved with high regioselectivity.

Recent synthetic additions to the visible light photoredox catalysis toolbox

The boom in visible light photoredox catalysis (VLPC) research has demonstrated that this novel synthetic approach is here to stay. VLPC enables reactive radical intermediates to be catalytically generated at ambient temperature, a feat not generally allowed through traditional pyrolysis- or radical initiator-based methodologies. VLPC has vastly extended the range of substrates and reaction schemes that have been traditionally the domain of radical reactions. In this review the photophysics background of VLPC will be briefly discussed, followed by a report on recent inroads of VLPC into decarboxylative couplings and radical C-H functionalization of aromatic compounds. The bulk of the review will be dedicated to advances in synergistic catalysis involving VLPC, namely the combination of photoredox catalysis with organocatalysis, including β-functionalization of carbonyl groups, functionalization of weak aliphatic C-H bonds, and anti-Markovnikov hydrofunctionalization of alkenes; dual catalysis with gold or with nickel, photoredox catalysis as an oxidation promoter in transition metal catalysis, and acid-catalyzed enantioselective radical addition to π systems.

Visible-light-induced bromoetherification of alkenols for the synthesis of β-bromotetrahydrofurans and -tetrahydropyrans

A visible-light-induced photoredox-catalyzed bromoetherification of alkenols is described. This approach, with CBr4 as the bromine source through generation of bromine in situ, provides a mild and operationally simple access to the synthesis of β-bromotetrahydrofurans and -tetrahydropyrans with high efficiency and regioselectivity.

Visible light-induced difunctionalization of electron-enriched styrenes: synthesis of tetrahydrofurans and tetrahydropyrans

The difunctionalization of electron-enriched styrenes for the synthesis of substituted tetrahydrofurans and tetrahydropyrans in the presence of photoredox catalysts is described.