The mild reducing agent tetramethylammonium triacetoxyborohydride reduces acyclic ß-hydroxy ketones to their corresponding anti diols with high diastereoselectivity. a-Alkyl substitution does not significantly affect the stereoselectivity of these reductions. In all cases examined, good to excellent yields of diastereomerically homogeneous diols were obtained. The mechanism of these reductions involves an acid-promoted ligand exchange of acetate for substrate alcohol by the

The spiro[pyrrolidine‐3,3′‐oxindole] ring system is found at the core of a number of alkaloids, which possess significant biological activity and are interesting, challenging targets for chemical synthesis. In the present review, we report on the different strategies for the synthesis of the spiro[pyrrolidine‐3,3′‐oxindole] ring system in the context of recent synthesis of coerulescine, horsfiline, elacomine, salacin, pteropodine, alstonisine, spirotryprostatin A and B, and strychnofoline. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

We report an Ir(I)-catalyzed kinetic resolution of secondary allylic carbonates allowing for their isolation in up to 98% ee. Importantly, the study documents the synthesis and use of a new class of chiral [2.2.2]-bicyclooctadiene ligands for iridium.

Two for the price of one: Sulfamic acid serves not only as a nitrogen source but also as an in situ activator of hydroxy groups in the first direct iridium‐catalyzed synthesis of primary allylic amines from allylic alcohols (see scheme; cod=cycloocta‐1,5‐diene). The reaction is catalyzed by a commercially available iridium complex and a phosphoramidite‐based bidentate phosphorus–olefin ligand.

Oxidation of organic substrates by direct oxygen-atom transfer from transition-metal complexes is of fundamental importance and has been subject to intensive investigation. 1 Highly selective methods for alkene epoxidation and dihydroxylation have been described and are commonly employed in synthesis. 2,3 By contrast, significantly fewer reagents and protocols are available for the analogous nitrogen-atom-transfer process, despite the enormous potential utility of such methodology. 4 Recent efforts by other groups to develop general olefin amination strategies have led to impressive advances in both metalcatalyzed hydroxyamination and aziridination. 5,6 Our interest in this area has resulted in the preparation and characterization of novel nitridomanganese complexes which may be activated for nitrogen-atom transfer. Pivotal to the success of this research has been the development of new protocols for the construction of these manganese nitride (MntN) reagents. These systems have proven to be versatile and effective aminating agents with different classes of olefins which include both silyl enol ethers and glycals (eq 1). The following account documents these findings and highlights the unique chemistry of these complexes as nitrogen-atom-transfer reagents. BackgroundOur desire to develop novel nitrogen-atom-transfer reagents was fueled by the potential application of aziridi-nation and amination technologies for chemical synthesis together with the paucity of available strategies for effecting such transformations. 4,6 To this end, we became interested in a report by Groves of a nitridomanganese-(V) porphyrin system ((TMP)MntN) 2, which, when reacted with trifluoroacetic anhydride (TFAA), transferred CF 3 CON to cis-cyclooctene to furnish the N-trifluoroacetyl-protected aziridine 3 (Figure 1). 7 This example of a metal nitrenoid coupling with an olefin was unique and did not appear to be plagued by competing insertion and C-H abstraction reactions typically observed in processes thought to involve nitrenoid intermediates. 4,6a,i Additionally, because of the apparent similarity between this aziridination reaction and related oxo-transfer processes, it was thought that the expansive body of information on metal-catalyzed epoxidation reactions would provide an invaluable guide for the development of this work. 1a,8 In this regard, particular attention was paid to the numerous (1) (a)

Chemical tools and methods that report on G protein-coupled receptor (GPCR) expression levels and receptor occupancy by small molecules are highly desirable. We report the development of LEI121 as a photoreactive probe to study the type 2 cannabinoid receptor (CB2R), a promising GPCR to treat tissue injury and inflammatory diseases. LEI121 is the first CB2R-selective bifunctional probe that covalently captures CB2R upon photoactivation. An incorporated alkyne serves as ligation handle for the introduction of reporter groups. LEI121 enables target engagement studies and visualization of endogenously expressed CB2R in HL-60 as well as primary human immune cells using flow cytometry. Our findings show that strategically functionalized probes allow monitoring of endogenous GPCR expression and engagement in human cells using tandem photoclick chemistry and hold promise as biomarkers in translational drug discovery.

To dye for: A highly fluorescent, photostable aza‐dipyrromethene dye 1 (λem=751 nm) with sharp and intense absorption (full width at half maximum height=30.4 nm; ε=159 000) in the near‐infrared (NIR) region (λmax=740 nm) is reported. The dye is insensitive to solvent polarity, meets the requirements of a NIR chromophore, and has potential use in biological probes.

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