Synthesis of Secondary and Tertiary Alkyl Boronic Esters by gem -Carboborylation: Carbonyl Compounds as Bis(electrophile) Equivalents

Approach to the Synthesis of gem-Thiolated Alkylboronates via Cobalt-Catalyzed Diboration of Aldehydes

A new method has been developed for the sequential gem-thioborylation of readily available aldehydes via the cobalt-catalyzed diboration reaction. The N-heterocyclic carbene (NHC)-cobalt complex has been used as a catalyst for the diboration of aldehydes to generate α-oxyl boronic esters, which react with lithium thiolates to form a tetracoordinate boronate species, which undergoes 1,2-metalate rearrangement in the presence of trifluoroacetic anhydride. The stepwise functionalization of the boryl and thiol moiety of the products enriches the chemical toolbox of diverse organic synthesis.

Triflylpyridinium Enables Rapid and Scalable Controlled Reduction of Carboxylic Acids to Aldehydes using Pinacolborane

Building up new and efficient methods for the controlled conversion of carboxylic acids to aldehydes is important. Herein, we report a rapid, modular and scalable method for the conversion of carboxylic acids to aldehydes using pinacolborane at ambient temperature, in which a triflylpyridinium reagent is used. The conversion of carboxylic acid to intermediate acylpyridinium by triflylpyridinium is new. A binary pyridine-coordinated boronium complex is generated after reduction. The unprecedented reduction of the acylpyridinium by HBpin opens up a practically direct synthesis of aldehydes from carboxylic acids. Theoretical studies indicate that the reduction of acylpyridinium requires a lower activation free energy than that of the product aldehyde. The synthetic advantage of this protocol is further highlighted by the scalable synthesis of aldehyde via continuous flow process. Configuration retention for chiral acids are presented in those syntheses.

Deoxygenative Functionalizations of Aldehydes, Ketones and Carboxylic Acids

Conversion of carbonyl compounds, including aldehydes, ketones and carboxylic acids, into functionalized alkanes via deoxygenation would be highly desirable from a sustainability perspective and very enabling in chemical synthesis. This review covers the recent methodology development in carbonyl and carboxyl deoxygenative functionalizations, highlighting some typical and significant contributions in this field. These advances will be categorized based on types of bond formation, and in each part, selected examples will be discussed from their generalized mechanistic perspectives. Four summarized reactivity modes of aldehydes and ketones during the deoxygenation, namely, bis-electrophile, carbenoid, bis-nucleophile and alkyl radical, are presented, while the carboxylic acids are deoxygenated mainly via activated carbonyl or acetal intermediates.

Aminoazanium of DABCO: An Amination Reagent for Alkyl and Aryl Pinacol Boronates

The aminoazanium of DABCO (H₂ N-DABCO) has been developed as a general and practical amination reagent for the direct amination of alkyl and aryl pinacol boronates. This compound is stable and practical for use as a reagent. Various primary, secondary. and tertiary alkyl-Bpin and aryl-Bpin substrates were aminated to give the corresponding amine derivatives. The amination is stereospecific. The anti-Markovnikov hydroamination of olefins was easily achieved by catalytic hydroboration with HBpin and in subsequent situ amination using H₂ N-DABCO. Moreover, the combination of 1,2-diboration of olefins, using B₂ pin₂ , with this amination process achieved the unprecedented 1,2-diamination of olefins. The amination protocol was also successfully extended to aryl pinacol boronates.