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A photoredox approach enabling one-step synthesis of oxazetidines with a free –NH group via the combined use of alkyne, thiophenol, and azide has been reported.

A visible light-mediated approach enabling the use of alcohols as nucleophiles in a one-step synthesis of α-alkoxy/hydroxy diarylacetaldehydes is reported.

A photoredox approach enabling one-step synthesis of oxazetidines with a free -NH group

Visible light mediated functionalizations have significantly expanded the scope of alkynes by unraveling new mechanistic pathways and enabling their transformation to diverse structural entities. The photoredox reactions on alkynes rely on their innate capability to generate myriad carbon-centred radicals via single electron transfer (SET), thereby, allowing the introduction of new radical precursors. Moreover, an array of methods have been developed facilitating transformations such as vicinal or gem-difunctionalization, annulation, cycloaddition and oxidative reactions to construct numerous key building blocks of natural and pharmaceutically important molecules. In addition, the introduction of photoredox chemistry has successfully been used to deal with the challenges associated with alkyne functionalization such as stereoselective and regioselective control. This article accounts for several visible light mediated functionalization reactions of alkynes, wherein they have been transformed into α-oxo compounds, β-keto sulfoxides, substituted olefins, N-heterocycles, internal alkynes and sulfur containing compounds. The article has been primarily categorized into various sections based on the reaction type with particular attention being paid to mechanistic details, advancement and future applications.

A first procedure on the synthesis of dibenzo-1,7-naphthyrdine carboxylate via photoredox catalysis has been developed. The reaction features an umpolung reaction of C-3 keto group and entrapment of decarbonylation prone C-2 of isatin. Additionally, the method showcases chemo-divergent behaviour of isatins in aprotic solvents leading to synthesis of tryptanthrin derivatives via photoredox catalysis. The reaction is easy to set up and scalable to gram levels.

A photoredox catalyzed approach enabling use of alkynes as surrogate of 2-oxoaldehydes/1,2-diones is reported. The method overcomes the difficulty associated with application of unsubstituted aliphatic α-oxoaldehydes, which has hitherto limited their general use. Indoles, tryptamine, and tryptophan methyl ester participated in the reaction to give a variety of α-oxo based analogues. Quantum yield investigations support a radical chain mechanism.

A highly efficient Cu–Mn-catalyzed process for the aminolysis of esters was developed. Also, the catalyst promoted the self- and cross-dehydrogenative coupling of anilines to generate symmetrical and unsymmetrical azobenzenes, respectively. The reactions were performed under neutral conditions with an inexpensive catalyst, gave high yields, and offered wide functional group tolerance.

A simple and practical method for synthesizing α-ketoamides has been developed involving Cu(OTf)2-promoted oxidative amidation-diketonization of terminal alkynes with primary/secondary amines. This method has a wide substrate scope, and atmospheric oxygen acts as the oxidant.

An efficient metal free self-sorting tandem protocol for stereospecific synthesis of 2-thio-1,4-enediones involving C-C double bond formation via direct coupling of terminal alkynes has been developed. The method was also extended to the first synthesis of β-thio-γ-keto-α,β-unsaturated esters via a cross coupling reaction with ethyl glyoxylate. The reaction relies on a first of its kind use of Bronsted and Lewis acids to switch selectivity for the synthesis of an E or a Z-isomer respectively.

(S)-1,1′-Binaphthyl-2,2′-diol was prepared in high optical purity (∼98%) via Arthrobacter sp. lipase (MTCC No. 5125) catalyzed kinetic resolution. The immobilization of the substrate on a solid inert support significantly improved the enantioselectivity factor (E) by almost sixfolds, i.e. from ∼27 to >180. The effect of acyl substituents and co-solvents were also studied.

This short review highlights the various methods of formation of tetrahydropyranyl ethers (THPEs) as a method for the protection of simple alcohols as well as a diverse range of complex molecules using a variety of reagents and reaction conditions, i.e., acid catalyst, heterogeneous catalyst and neutral reagent mediated reactions. We also discuss their direct conversion to other useful functionalities.

A mild and highly chemoselective approach to oxidation of allylic, electron rich/deficient benzylic, and heterocyclic alcohols employing catalytic quantities of K2[OsO2(OH)4] (3 mol %) and chloramine-T (50 mol %) is described. The protocol offers short reaction times (25 min–2 h), controlled oxidation, and tolerance to a variety of substrates. A systematic mechanistic study based on the LC-ESI-MS/MS reveals the presence of imidotriooxoosmium species which further reacts with alcohol to give the oxidized product.

A facile and scalable methodology for the preparation of optically active (3S)-1-benzylpyrrolidin-3-ol (3), an important drug precursor, is reported. Starting from the naturally occurring alkaloid (−)-vasicine (1), a major alkaloid of the plant Adhatoda vasica, 3 was obtained in 84% overall yield (Scheme 3).

A highly efficient Cu–Mn-catalyzed process for the aminolysis of esters was developed. Also, the catalyst promoted the self- and cross-dehydrogenative coupling of anilines to generate symmetrical and unsymmetrical azobenzenes, respectively. The reactions were performed under neutral conditions with an inexpensive catalyst, gave high yields, and offered wide functional group tolerance.

Received: December 30, 2010; Revised: February 23, 2011; Published online: May 17, 2011Supporting information for this article is available on the WWW underhttp://dx.doi.org/10.1002/adsc.201000980.Abstract: The lipase Novozym435 (0.6% w/w) wasused in tandem with organocatalysts in a first vinyl/isopropenyl acetate-mediated aldol reaction. Thereaction was facilitated through the lipase-catalyzedin situ generation of acetaldehyde/acetone. The im-portant features of the present methodology includethe mild and facile reaction conditions, regenerabili-ty of the lipase, comparatively high yields and mini-mal side product formation.Keywords: acetaldehyde; catalysis; cross-aldol reac-tion; proline; triethylamine; vinyl acetateTandem catalysis involving biocatalysts such as lipaseshas recently generated considerable interest due tothe enhanced efficacy of the reaction process andease of handling, preferably in a single reactor. Atandem reaction process offers certain advantagesover multistep synthetic operations. One of the moststudied tandem catalysis displaying synthetic utility isthe lipase- and metal-catalyzed dynamic kinetic reso-lution (DKR) of secondary alcohols.

The expedient synthesis of enantiopure masked 1,2-amino alcohols (ee >99%) including their alkyl substituted analogues has been achieved by the regioselective ring opening of epoxides using phthalimide, followed by highly efficient kinetic resolution under mild and environmentally friendly conditions. The addition of co-solvents during kinetic resolution significantly improved the enantioselectivity with reduction in time.

In the presence of atmospheric oxygen, secondary and primary amines can be used in the title process.

In the presence of trimethylsilyl triflate and catalytic amounts of iodine, the first metal free oxidative amidation—diketonization of terminal alkynes leads to a wide variety of α-ketoamides.

This short review highlights the various methods of formation of tetrahydropyranyl ethers (THPEs) as a method for the protection of simple alcohols as well as a diverse range of complex molecules using a variety of reagents and reaction conditions, i.e., acid catalyst, heterogeneous catalyst and neutral reagent mediated reactions. We also discuss their direct conversion to other useful functionalities.

A novel catalytic system TMSOTf/I2/DMSO for the oxidative coupling of terminal alkynes with virtually any primary/secondary amine leading to α-ketoamides has been developed. The reaction possibly proceeds via iminium ion formation, wherein DMSO acts as a solvent as well as an oxidizing agent.

The novel method is advantageous with regards to chemoselectivity, short reaction times, and tolerance towards a variety of substrates.

Novozym435/NEt3-catalyzed treatment of isopropenyl acetate with aromatic aldehydes is found to allow new, mild, and efficient access to β-hydroxy ketones.

β-Amino alcohols are bioactive molecules, used also as catalysts in asymmetric C–C bond formation. While asymmetric synthesis has been the preferred route for their preparation, there was always been a need to develop a facile methodology involving environmentally friendly transformations. Masked amines in the form of phthalimide alcohols, prepared via a fast coupling reaction in an ionic liquid as a reusable reaction media together with reduction and an efficient biocatalytic resolution, offer a green methodology for enantiomerically pure products (ee > 99%, 50 g L−1).

Molecular iodine catalyzes acetalation and acetylation of reducing sugars and sugar glycosides with stoichiometric amounts of enol acetates under solvent-free conditions, thereby facilitating the synthesis of various types of orthogonally protected sugar derivatives in short time and good yields. The outcome of the reaction can be controlled by variation in temperature. Thus at lower temperature, it is possible to obtain the acetonide acetate as a single product whereas peracetate is the major product at higher temperature.

The substrate/lipase ratio as well as pH of the buffer medium played important roles in the resolution of geometrical isomeric mixture of geraniol–nerol. Based on the results, an immobilized lipase...

β-Amino alcohols are bioactive molecules, used also as catalysts in asymmetric C–C bond formation. While asymmetric synthesis has been the preferred route for their preparation, there was always been a need to develop a facile methodology involving environmentally friendly transformations. Masked amines in the form of phthalimide alcohols, prepared via a fast coupling reaction in an ionic liquid as a reusable reaction media together with reduction and an efficient biocatalytic resolution, offer a green methodology for enantiomerically pure products (ee > 99%, 50 g L−1).