Iridium-catalyzed enantioselective alkynylation and kinetic resolution of alkyl allylic alcohols

Herein, we report an efficient kinetic resolution of alkyl allylic alcohols enabled by an iridium-catalyzed enantioselective alkynylation of alkyl allylic alcohols with potassium alkynyltrifluoroborates. A wide range of chiral 1,4-enynes bearing various functional groups and unreacted enantioenriched allylic alcohols were obtained with excellent enantioselectivities and high kinetic resolution performance (s-factor up to 922). Additionally, this method is particularly effective for preparing some useful optically pure alkyl allylic alcohols, such as the key components towards the synthesis of prostaglandins and naturally occurring matsutakeols, which are difficult to access via other asymmetric reactions. Mechanistic studies revealed that the efficient kinetic resolution might be due to the significant distinction of the η ²-coordination between the (R)- and (S)-allylic alcohols with the iridium/(phosphoramidite, olefin) complex.

Direct deoxygenation of active allylic alcohols via metal-free catalysis

Direct metal-free deoxygenation of highly active allylic alcohols catalyzed by a Brønsted acid was achieved, which avoids tedious reaction steps and eliminates metal contamination. By examining a series of Brønsted...

Iridium-catalyzed highly stereoselective deoxygenation of tertiary cycloalkanols: stereoelectronic insights and synthetic applications

Excellent and unique diastereoselectivity is observed in the iridium-catalyzed deoxygenation of tertiary cyclohexanols and cyclopentanols. The substituent effect on the diastereoselectivity and detailed control models are analyzed case by case, using tertiary monocyclic and polycyclic cyclohexanols, bicyclic bridged cycloalkanols, and cyclopentanols as the model substrates. The selectivity is decided by the steric environment of the carbocation intermediates and is independent of the catalyst loading. Stereoelectronically, the iridium hydride approaches the carbocation in directions perpendicular to the carbocation plane. The sterically large iridium hydride delivers its hydride in the sterically least hindered direction to the carbocation. The deoxygenation has found important applications in the stereospecific arylations of sterically complex compounds. Our deoxygenation is stereochemically very different from the coupling reactions and can be used to specifically synthesize stereoisomers that are not available via cross-couplings.

Silver-Catalyzed [2+1] Cyclopropenation of Alkynes with Unstable Diazoalkanes: N-Nosylhydrazones as Room-Temperature Decomposable Diazo Surrogates

The [2+1] cycloaddition of alkynes with diazo compounds represents one of the most powerful and reliable methods for the construction of cyclopropenes. However, it remains a formidable challenge to accomplish the cyclopropenation of alkynes with non-stabilized diazoalkanes, owing to the fact that such compounds are unstable and prone to detonation. Herein, we report a general silver-catalyzed cyclopropenation reaction of alkynes with unstable diazoalkanes, by for the first time the discovery and application of N-nosylhydrazones as room-temperature decomposiable diazo surrogates. This method allows for the efficient assembly a wide variety of cyclopropene derivatives that are otherwise difficult to access by conventional methods.

Silver(i)-promoted insertion into X–H (X = Si, Sn, and Ge) bonds with N-nosylhydrazones

Silver(i)-promoted carbene insertion into X–H (X = Si, Sn, and Ge) bonds has been realized by using unstable diazo compounds, which are generated in situ from N-nosylhydrazones as carbene precursors.