A Boron–Boron Double Transborylation Strategy for the Synthesis of gem-Diborylalkanes

Olefin hydroboration reactions provide efficient access to synthetically versatile and easily handled organoboronic esters. In this study, we demonstrate that the commercially available organoborane reagent 9-borabicyclo[3.3.1]nonane (H-B-9-BBN) can serve as a catalyst for the sequential double hydroboration of alkynes using pinacolborane (HBpin). This strategy, which is effective for a wide range of terminal alkynes, is predicated upon a key C(sp3)-B/B-H transborylation reaction. Transition-state thermodynamic parameters and 10-boron-isotopic labeling experiments are indicative of a σ-bond metathesis exchange pathway

Boron-Catalyzed, Diastereo- and Enantioselective Allylation of Ketones with Allenes

The diastereo- and enantioselective allylation of ketones remains a synthetic challenge, with transition metal catalysis offering the most applied methods. Here, a boron-catalyzed allylation of ketones with allenes is presented. Excellent yield, regioselectivity, and diastereoselectivity were found across functionalized substrates. The reaction was further developed to accommodate an enantioenriched boron catalyst and thus gave asymmetric ketone allylation in good yield, diastereoselectivity, and enantioselectivity. Mechanistic studies supported a hydroboration–allylation–transborylation pathway.S.P.T. acknowledges the Royal Society for a University Research Fellowship (URF/R/191015). S.P.T. and K.N. thank AstraZeneca and EPSRC for an iCase PhD studentship

A boron-oxygen transborylation strategy for a catalytic Midland reduction

The enantioselective hydroboration of ketones is a textbook reaction requiring stoichiometric amounts of an enantioenriched borane, with the Midland reduction being a seminal example. Here, a turnover strategy for asymmetric catalysis, boron.oxygen transborylation, has been developed and used to transform the stoichiometric borane reagents of the Midland reduction into catalysts. This turnover strategy was demonstrated by the enantioselective reduction of ketones, including derivatives of biologically active molecules and those containing reducible groups. The enantioenriched borane catalyst was generated in situ from commercially available reagents, 9-borabicyclo[3.3.1]nonane (H-B-9-BBN) and β-pinene, and B.O transborylation with pinacolborane (HBpin) was used for catalytic turnover. Mechanistic studies indicated that B.O transborylation proceeded by B.O/B.H boron exchange through a stereoretentive, concerted transition state, resembling σ-bond metathesis

B–N/B–H Transborylation: borane-catalysed nitrile hydroboration

The reduction of nitriles to primary amines is a useful transformation in organic synthesis, however, it often relies upon stoichiometric reagents or transition-metal catalysis. Herein, a borane-catalysed hydroboration of nitriles to give primary amines is reported. Good yields (48–95%) and chemoselectivity (e.g., ester, nitro, sulfone) were observed. DFT calculations and mechanistic studies support the proposal of a double B–N/B–H transborylation mechanism

Overstating the evidence - double counting in meta-analysis and related problems

Background: The problem of missing studies in meta-analysis has received much attention. Less attention has been paid to the more serious problem of double counting of evidence. Methods: Various problems in overstating the precision of results from meta-analyses are described and illustrated with examples, including papers from leading medical journals. These problems include, but are not limited to, simple double-counting of the same studies, double counting of some aspects of the studies, inappropriate imputation of results, and assigning spurious precision to individual studies. Results: Some suggestions are made as to how the quality and reliability of meta-analysis can be improved. It is proposed that the key to quality in meta-analysis lies in the results being transparent and checkable. Conclusions: Existing quality check lists for meta-analysis do little to encourage an appropriate attitude to combining evidence and to statistical analysis. Journals and other relevant organisations should encourage authors to make data available and make methods explicit. They should also act promptly to withdraw meta-analyses when mistakes are found