In this review, the recent advances of the application of 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene (4CzIPN) as a photoredox catalyst in the past three years (2016–2018) for various organic reactions are summarized.

The first efficient intermolecular reaction of gold carbene intermediates generated via gold-catalyzed alkyne oxidation has been realized using nitriles as both the reacting partner and the reaction solvent, offering a generally efficient synthesis of 2,5-disubstituted oxazoles with broad substrate scope. The overall reaction is a [2 + 2 + 1] annulation of a terminal alkyne, a nitrile, and an oxygen atom from an oxidant. The reaction conditions are exceptionally mild, and a range of functional groups are easily tolerated. With complex and/or expensive nitriles, only 3 equiv could be sufficient to achieve serviceable yields in the absence of any solvent and using only 1 mol % BrettPhosAuNTf(2) as the catalyst.

A general solution for the synthesis of various oxetan-3-ones is developed. This reaction uses readily available propargylic alcohols as substrates and proceeds without the exclusion of moisture or air ('open flask'). Notably, oxetan-3-one, a highly valuable substrate for drug discovery, can be prepared in one-step from propargyl alcohol in a fairly good yield. The facile formation of the strained oxetane ring provides strong support for the intermediacy of α-oxo gold carbenes. This safe and efficient generation of gold carbenes via intermolecular alkyne oxidation offers a potentially general entry into α-oxo metal carbene chemistry without using hazardous diazo ketones.Oxetan-3-ones1 contain a strained four-membered ring and possess considerable synthetic/ medicinal utility. They have been incorporated into steroid skeletons,2 used to prepare oxetanocin derivatives,3 and converted into 3-aminooxetanes4 including 3-aminooxetane-3-carboxylic acid.4a Moreover, Rogers-Evans, Carreira and co-workers have shown that the oxetane ring can serve as a surrogate of a gem-dimethyl group,5a resemble a carbonyl group,5b and offer alternatives to 1,3-heteroatom-substituted cyclohexanes in spirocyclic structures5c in drug discovery; in these studies, the parent oxetan-3-one serves as an essential starting material for introducing the oxetane ring. However, synthesis of oxetan-3-ones typically demand multiple synthetic steps and/or highly functionalized substrates.1 For example, oxetan-3-one itself was prepared in 45a or 54 steps with 23% or 13% overall yield, respectively, highlighting the challenge of constructing this strained skeleton and the lack of efficient preparative methods.α-Diazo ketones have been used to prepare oxetan-3-ones (Scheme 1),6 but those diazo substrates are in general hazardous and their preparations are non-trivial. We have recently developed a practical and efficient synthesis of dihydrofuran-3-ones via gold-catalyzed intermolecular oxidation of terminal alkynes,7 where a C-C triple bond is converted into a reactive α-oxo gold carbene intermediate in the proposed catalytic cycle. This strategy would render alkynes equivalent to α-diazo ketones in accessing α-oxo metal carbene chemistry,8 which could offer significant synthetic and economic benefits. We speculated * zhang@chem.ucsb.edu . Supporting Information Available:Experimental procedures, compound characterization data. This material is available free of charge via the Internet at http://pubs.acs.org. that this equivalency could substitute the α-diazo ketone moiety in oxetan-3-one synthesis6 with a simple C-C triple bond (Scheme 1); as a result, readily available propargylic alcohols could serve as direct substrates. Herein, we report a successful implementation of the design and the development of a practical solution to oxetan-3-one synthesis; moreover, the ease of forming this strained ring provides convincing support for the formation of α-oxo gold carbene intermediates via intermolecular alkyne oxidation. NIH Public AccessPropargylic...

Small ring made easy and chiral Chiral azetidin-3-ones could be easily prepared from chiral N-propargylsulfonamides, which in turn are readily accessible in excellent e.e. via chiral sulfinamide chemistry. Using t-butanesulfonyl as the protecting group avoids unnecessary deprotection and reprotection and allows its removal from the azetidine ring under acidic conditions.

A facile, practical and eco-friendly protocol for the synthesis of various Z-vinyl thiocyanates under minimal solvent conditions was developed.

The first example of direct synthesis of 2-sulfonylquinolines through visible-light-induced deoxygenative C2-sulfonylation of quinoline N-oxides with organic dye as the catalyst and ambient air as the sole oxidant was developed.

α-Oxo gold carbenes generated via intermolecular oxidation of terminal alkynes are shown to be highly electrophilic and can effectively abstract halogen from halogenated solvents such as 1,2-dichloroethane or 1,2-dibromoethane. Chloro/bromomethyl ketones are prepared in moderate efficiencies in one step using Ph(3)PAuNTf(2) as the catalyst and 8-methylquinoline N-oxide as the oxidant.

A general atom-economical approach for the synthesis of α-halomethyl ketones is demonstrated through hydration of a wide range of haloalkynes. Other outstanding features include excellent yields from both alkyl- and aryl-substituted haloalkynes and wide functional group tolerance. This protocol is an alternative to conventional α-halogenation of ketones.