The first Ir-catalyzed C-H borylation (CHB) of amidine aliphatic bonds is reported. The products can be isolated as boronic esters as well as air stable difluoroborate molecules. Selectivity for primary as well as secondary N-adjacent C(sp(3))-H bonds is demonstrated even in the presence of sterically accessible C(sp(2))-H and other C(sp(3))-H bonds. Monoborylation occurs when the amidine is the limiting reagent versus the boron source.

An acid-catalyzed [1,2]-carbon-to-carbon silyl migration is reported for the synthesis of α-silyl aldehydes from α-hydroxy allyl silanes, which can serve as valuable precursors for various organic reactions. During the synthesis of α-hydroxy allyl silanes, an unexpected aldehyde peak in NMR suggested an in situ rearrangement, later confirmed to be acid-driven. Expanding the substrate scope revealed that an alkyl substituent at the β-position was crucial for migration. Mechanistic studies indicated a stepwise process via a carbocation intermediate, as confirmed by stereochemical erosion in enantiomerically enriched substrates. The tertiary carbocation is further stabilized by the β-silicon effect. The advantages of this method include mild reaction conditions, clean conversion, and often no need for purification.

Radicals have long fascinated chemists owing to their structure, reactivity, and other features. The recent discovery of frustrated radical pairs (FRPs) has added a new dimension to this field. These unique radicals, which do not conform to traditional radical behavior, have opened a world of intriguing possibilities. FRPs have been categorized into neutral and ionic frustrated radical pairs and both are addressed as FRPs in this review. These pairs consist of two different (transient and persistent) radicals or radical ion pairs that do not react with each other. Such orthogonal reactivities and the resultant "persistent radical effect" enable chemical transformations that are difficult to achieve using traditional radical chemistry. This highlight uses recent examples to explore the different ways of generating these radical pairs and their working principle, highlighting the novelty and potential of this emerging field.

Despite being an important aromatic amino acid, iridium-catalyzed borylation (CHB) of levodopa has not been reported. Via the application of carefully chosen protecting groups for the catechol moiety, the steric hindrance around the arene can be reduced, enabling selective C5 CHB of levodopa. Methylene and boronic ester protecting groups were explored, the latter of which is deprotected in situ to yield the free catechol.

Hydrosilylation of double-decker silsesquioxanes is an efficient approach for preparing hybrid materials, especially polymeric materials. Karstedt's catalyst, Pt(dvs), is widely used for this purpose due to its commercial availability, high yields, and good hydrosilylation selectivity. Despite this, vinylbenzenes have been shown to produce multiple hydrosilylated products. This study employs a method involving an iridium catalyst that was significantly more selective for the anti-Markovnikov hydrosilylation product with vinylbenzenes and bis-silane-capped double-decker silsesquioxanes. Obtaining higher purity of hydrosilylated products will allow for the development of the fundamental structure-property relationship of hybrid materials.

Ir-catalyzed arene C-H borylations (CHB) of anilines can be highly ortho selective by using a small B2eg2 (eg = ethane-1,2-diol) as the borylating reagent. Unfortunately, the products are prone to decomposition, and transesterification with pinacol is required prior to isolation. This work offers a solution by adjusting the size of the diboron reagent. Based on our evaluation, we conclude that B2bg2 (bg = butane-1,2-diol) achieves an optimal balance between CHB regioselectivity and stability for the borylated products.

This paper presents a simple and cost-effective hydrogenation method for synthesizing a myriad of cycloalkanes and saturated heterocycles bearing boryl or silyl substituents. The catalyst used are heterogeneous, readily available, bench stable, and recyclable. Also demonstrated is the application of the method to compounds that possess both boryl and silyl groups. When combined with Ir-catalyzed sp2 C-H borylation, such hydrogenations offer a two-step complementary alternative to direct sp3 C-H borylations that can suffer selectivity and reactivity issues. Of practical value to the community, complete stereochemical analyses of reported borylated compounds that were never fully characterized are reported herein.

Two reported methods for protecting the catechol moiety of L-DOPA as an acetonide have been compared. NMR spectral data and crystal structure analysis confirmed that in contrast to that indicated in Greene's Protective Groups in Organic Chemistry the conditions reported for the direct conversion of L-DOPA into its acetonide give instead, a Pictet-Spengler derived tetrahydroisoquinoline.

Tetraalkoxydiborons can be easily prepared by acid-catalyzed reactions of tetrahydroxydiboron or its anhydride with trialkyl orthoformates. Addition of diols to these reaction mixtures afforded diboron diolates in high yield. In both cases, removal of volatile byproducts is all that is required for the isolation of the diboron. These methods constitute a convenient alternative to previous preparations from tetrakis (dimethylamino) diboron and tetrahydroxydiboron.

Ir-catalyzed C-H borylations of fluorinated and cyanated arenes with high meta-to-F/CN are described. Use of a dipyridyl hydrazone framework as the ancillary ligand and pinacolborane (HBpin) as the functionalizing reagent generates catalysts that are significantly more active and selective than 4,4'-di-tert-butyl-2,2'-bipyridine (dtbpy) for both electron-deficient and electron-rich substrates. Investigation of the ligand framework resulted in the observation of formal N-borylation of the hydrazone by HBpin, as evidenced by NMR spectroscopy and X-ray crystallography. Subsequent stoichiometric reactions of this adduct with an iridium precatalyst revealed the formation of an unusual IrI hydrazido. Isolation and use of this hydrazido reproduce the selectivity of in situ generated catalysts, suggesting that it leads to formation of the active species.

Traditional reaction conditions in Ir-catalyzed C-H borylation consist of a 2:1 ligand to Ir metal ratio, affording C(sp2)-H borylation at the least sterically hindered position. We found that lowering the ligand to metal ratio of a N,B-type diboron (BB) preligand in respect to the IrI precatalyst to 0.5:1 affords the chelate controlled ortho product. Switching from steric-directed to chelate-directed products is shown for various substituted arenes and (hetero)arenes containing Lewis-basic functionalities. This work offers the first example of obtaining complementary regioisomers as the major product by altering the ligand loading in CHB.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

A bidentate monoanionic ligand system was developed to enable iridium catalyzed C(sp3)–H activation borylation of N-methyl amides. Borylated amides were obtained in moderate to good isolated yields, and exclusive mono-borylation allowed the amide to be the limiting reagent. Selectivity for C(sp3)–H activation was demonstrated in the presence of sterically available C(sp3)–H bonds. Competitive kinetic isotope studies revealed a large primary isotope effect, implicating C–H activation as the rate limiting step.

Regioselectivities in catalytic C-H borylations (CHBs) have been rationalized using simplistic steric models and correlations with nuclear magnetic resonance (NMR) chemical shifts. However, regioselectivity can be significant for important substrate classes where none would be expected from these arguments. In this study, intramolecular hydrogen bonding (IMHB) can lead to steric shielding effects that can direct Ir-catalyzed CHB regiochemistry. Bpin (Bpin = pinacol boronic ester)/arene IMHB can promote remote borylations of N-borylated anilines, 2-amino-N-alkylpyridine, tetrahydroquinolines, indoles, and 1-borylated naphthalenes. Experimental and computational studies support molecular geometries with the Bpin orientation controlled by a C-H⋯O IMHB. IMHB-directed remote CHB appeared operative in the C6 borylation of 3-aminoindazole (seven-membered IMHB) and C6 borylation of an osimertinib analogue where a pyrimidine IMHB creates the steric shield. This study informs researchers to evaluate not only inter- but also intramolecular noncovalent interactions as potential drivers of remote CHB regioselectivity.

A versatile and efficient method to prepare borylated arenes furnished with alkyl, alkenyl, alkynyl, aryl, and heteroaryl functional groups is developed by merging Ir-catalyzed C-H borylations (CHB) with a chemoselective palladium-catalyzed cross-coupling of triorganoindium reagents (Sarandeses-Sestelo coupling) with aryl halides bearing a boronic ester substituent. Using triorganoindium cross-coupling reactions to introduce unsaturated moieties enables the synthesis of borylated arenes that would be difficult to access through the direct application of the CHB methodology. The sequential double catalyzed procedure can be also performed in one vessel.

Bisfunctional dichlorosilanes were reacted with tetrasilanol of double-decker shaped octaphenylsilsesquioxane (DDSQ) to form fully condensed DDSQ compounds. The crystallographic and thermal characteristics of these compounds were examined. For compounds capped with dichlorosilanes bearing linear aliphatic moieties, as the number of carbon increases from methyl to n -butyl (from 1 to 4) the melting temperature, T m , dropped from 546 K to 416 K. While for compounds capped with cycloaliphatic, as the moiety changes from cyclopentyl to cyclohexyl, the value of T m increases from 533 K to 555 K. Surprising, the highest T m observed was that when capping was done using diisopropyl dichlorosilane. A T m of around 565 K was observed, which was even higher as compare to diphenyl dichlorosilane capped DDSQ, which had T m of about 526 K. Phase behavior of binary and ternary mixtures of these condensed DDSQ was also investigated. To our surprise, mixtures of these compounds form eutectic. The eutectic points were calculated based on ideal binary and ternary eutectic from the thermal properties of pure components. Depending on the crystallography, experimental observations of eutectic match well with calculated values.

4-Silyl-5,6-dihydropyrans undergo remarkably selective [1,4]-Wittig rearrangements to give silylcyclopropanes in good yields. The selectivity is independent of the silyl group, but it is influenced by the electronic character of the migrating center. Electron-rich and electron-neutral (hetero)aryl groups and aliphatic substituents at the migrating center lead to exclusive [1,4]-migration, whereas electron-deficient aryl groups predominantly afford [1,2]-Wittig products.

Borylated aryl alkynes have been synthesized via one-pot iridium catalyzed C–H borylation (CHB)/Sonogashira cross-coupling of aryl bromides. Direct borylation of aryl alkynes encountered problems related to the reactivity of the alkyne under CHB conditions. However, tolerance of aryl bromides to CHB made possible a subsequent Sonogashira cross-coupling to access the desired borylated aryl alkynes.

By modifying ligand steric and electronic profiles it is possible to C-H borylate ortho or meta to substituents in aromatic and heteroaromatic compounds, where steric differences between accessible C-H sites are small. Dramatic effects on selectivities between reactions using B2pin2 or 4,4,5,5-tetramethyl-1,3,2-dioxaborolane (HBpin) are described for the first time. Judicious ligand and borane combinations give highly regioselective C-H borylations on substrates where typical borylation protocols afford poor selectivities.