Enantioselective α-Boryl Carbene Transformations.

Carbenes, recognized as potent intermediates, enable unique chemical transformations, and organoborons are pivotal in diverse chemical applications. As a hybrid of carbene and the boryl group, α-boryl carbenes are promising intermediates for the construction of organoborons; unfortunately, such carbenes are hard to access and have low structural diversity with their asymmetric transformations largely uncharted. In this research, we utilized boryl cyclopropenes as precursors for the swift synthesis of α-boryl metal carbenes, a powerful category of intermediates for chiral organoboron synthesis.

Iron-Catalyzed Allylic C(sp)-H Silylation: Spin-Crossover-Efficiency-Determined Chemoselectivity.

The nuanced role of spin effects remains a critical gap in designing proficient open-shell catalysts. This study elucidates an iron-catalyzed allylic C(sp)-H silylation/alkyne hydrosilylation reaction, in which the spin state of the open-shell iron catalyst dictates the reaction kinetics and pathway. Specifically, spin crossover led to alkyne hydrosilylation, whereas spin conservation resulted in a novel allylic C(sp)-H silylation reaction.

Iron-Catalyzed C(sp)-C(sp) Coupling to Construct Quaternary Carbon Centers.

The construction of quaternary carbon centers via C-C coupling protocols remains challenging. The coupling of tertiary C(sp) with secondary or tertiary C(sp) counterparts has been hindered by pronounced steric clashes and many side reactions. Herein, we have successfully developed a type of bisphosphine ligand iron complex-catalyzed coupling reactions of tertiary alkyl halides with secondary alkyl zinc reagents and efficiently realized the coupling reaction between tertiary C(sp) and secondary C(sp) with high selectivity for the initial instance, which provided an efficient method for the construction of quaternary carbon centers with high steric hindrance.

Iron-Catalyzed Stereoconvergent 1,4-Hydrosilylation of Conjugated Dienes.

Stereoconvergent transformation of E/Z mixtures of olefins to products with a single steric configuration is of great practical importance but hard to achieve. Herein, we report an iron-catalyzed stereoconvergent 1,4-hydrosilylation reactions of E/Z mixtures of readily available conjugated dienes for the synthesis of Z-allylsilanes with high regioselectivity and exclusive stereoselectivity. Mechanistic studies suggest that the reactions most likely proceed through a two-electron redox mechanism.

Wittig/B─H insertion reaction: A unique access to trisubstituted -alkenes.

The Wittig reaction, which is one of the most effective methods for synthesizing alkenes from carbonyl compounds, generally gives thermodynamically stable -alkenes, and synthesis of trisubstituted -alkenes from ketones presents notable challenges. Here, we report what we refer to as Wittig/B─H insertion reactions, which innovatively combine a Wittig reaction with carbene insertion into a B─H bond and constitute a promising method for the synthesis of thermodynamically unstable trisubstituted -boryl alkenes. Combined with the easy transformations of boryl group, this methodology provides efficient access to a variety of previously unavailable trisubstituted -alkenes and thus provides a platform for discovery of pharmaceuticals.

Chiral -difluoroalkyl reagents: -difluoroalkyl propargylic borons and -difluoroalkyl α-allenols.

Chiral fluorinated reagents provide new opportunities for the discovery of drugs and functional materials because the introduction of a fluorinated group significantly alters a molecule's physicochemical properties. Chiral -difluoroalkyl fragments (R-CF-C*) are key motifs in many drugs. However, the scarcity of synthetic methods and types of chiral -difluoroalkyl reagents limits the applications of these compounds.

Highly Regio-, Stereo-, and Enantioselective Copper-Catalyzed B-H Bond Insertion of α-Silylcarbenes: Efficient Access to Chiral Allylic gem-Silylboranes.

Herein, we report the development of a method for highly regio-, stereo-, and enantioselective B-H bond insertion reactions of α-silylcarbenes generated from 1-silylcyclopropenes in the presence of a chiral copper(I)/bisoxazoline catalyst for the construction of chiral γ,γ-disubstituted allylic gem-silylboranes, which cannot be prepared by any other known methods. This reaction is the first highly enantioselective carbene insertion reaction of α-silylcarbenes ever to be reported. The method shows general applicability for various 3,3-disubstituted silylcyclopropenes and exclusively affords E-products.

Uncommon carbene insertion reactions.

Transition-metal-catalysed carbene insertion reaction is a straightforward and efficient protocol for the construction of carbon-carbon or carbon-heteroatom bonds. Compared to the intensively studied and well-established "common" carbene insertion reactions, including carbene insertion into C-H, Si-H, N-H, O-H, and S-H bonds, several "uncommon" carbene insertion reactions, including carbene insertion into B-H, Sn-H, Ge-H, P-H, F-H, C-C, and M-M bonds, have been neglected for a long time. However, more and more studies on uncommon carbene insertion reactions have been disclosed recently, and clearly demonstrate the great synthetic potential of these reactions.

Dirhodium-Catalyzed Enantioselective B-H Bond Insertion of gem-Diaryl Carbenes: Efficient Access to gem-Diarylmethine Boranes.

The scarcity of reliable methods for synthesizing chiral gem-diarylmethine borons limits their applications. Herein, we report a method for highly enantioselective dirhodium-catalyzed B-H bond insertion reactions with diaryl diazomethanes as carbene precursors. These reactions afforded chiral gem-diarylmethine borane compounds in high yield (up to 99 % yield), high activity (turnover numbers up to 14 300), high enantioselectivity (up to 99 % ee) and showed unprecedented broad functional group tolerance.

Insertion of Alkylidene Carbenes into B-H Bonds.

We have developed a protocol for insertion of alkylidene carbenes into the B-H bonds of amine-borane adducts, enabling, for the first time, the construction of C(sp)-B bonds by means of carbene-insertion reactions. Various acyclic and cyclic alkenyl borane-amine adducts were prepared from readily accessible starting materials in good to high yields and were subsequently subjected to a diverse array of functional group transformations. The unprecedented spiro B-N heterocycles prepared in this study have potential utility as building blocks for the synthesis of pharmaceuticals.

Highly Enantioselective O-H Bond Insertion Reaction of α-Alkyl- and α-Alkenyl-α-diazoacetates with Water.

Catalytic asymmetric reactions in which water is a substrate are rare. Enantioselective transition-metal-catalyzed insertion of carbenes into the O-H bond of water can be used to incorporate water into the stereogenic center, but the reported chiral catalysts give good results only when α-aryl-α-diazoesters are used as the carbene precursors. Herein we report the first highly enantioselective O-H bond insertion reactions between water and α-alkyl- and α-alkenyl-α-diazoesters as carbene precursors, with catalysis by a combination of achiral dirhodium complexes and chiral phosphoric acids or chiral phosphoramides.

Effects of Spartina alterniflora invasion on the communities of methanogens and sulfate-reducing bacteria in estuarine marsh sediments.

The effect of plant invasion on the microorganisms of soil sediments is very important for estuary ecology. The community structures of methanogens and sulfate-reducing bacteria (SRB) as a function of Spartina alterniflora invasion in Phragmites australis-vegetated sediments of the Dongtan wetland in the Yangtze River estuary, China, were investigated using 454 pyrosequencing and quantitative real-time PCR (qPCR) of the methyl coenzyme M reductase A (mcrA) and dissimilatory sulfite-reductase (dsrB) genes. Sediment samples were collected from two replicate locations, and each location included three sampling stands each covered by monocultures of P.