Ring walking is an important mechanistic phenomenon leveraged in many catalytic C-C bond forming reactions. However, ring walking has been scarcely studied under Buchwald-Hartwig amination conditions despite the importance of such transformations. An in-depth mechanistic study of the Buchwald-Hartwig amination is presented focussing on ligand effects on ring walking behavior. The ability of palladium catalysts to promote or inhibit ring walking is strongly influenced by the chelating nature of the ligand. In stark contrast, the resting state of the catalyst had no impact on ring walking behavior. Furthermore, the complexity of the targeted system enabled the differentiation between catalysts which undergo ring walking versus diffusion-controlled coupling. The insights gained in this study were leveraged to achieve desymmetrization of a tetrabrominated precursor. A small library of asymmetric 2,2′,7,7′-tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9’spirobifluorene (SpiroOMeTAD) derivatives were successfully synthesized using this strategy highlighting the ease with which libraries of these compounds can be accessed for screening.

Directed hydration of α-amino nitriles was achieved under mild conditions using simple carbohydrates as catalysts exploiting temporary intramolecularity. A broadly applicable procedure using both formaldehyde and NaOH as catalysts efficiently hydrated a variety of primary and secondary susbtrates, and allowed the hydration of enantiopure substrates to proceed without racemization. This work also provides a rare comparison of the catalytic activity of carbohydrates, and shows that the simple aldehydes at the basis of chemical evolution are efficient organocatalysts mimicking the function of hydratase enzymes. Optimal catalytic efficiency was observed with destabilized aldehydes, and with difficult substrates only simple carbohydrates such as formaldehyde and glycolaldehyde proved reliable.

Kinetic investigations can provide critical mechanistic information for the optimization of the reaction parameters and reaction development. Modern kinetic analyses such as RPKA and VTNA provide many advantages over traditional initial rate methods and are especially powerful when coupled with reaction monitoring technologies. While these are robust analytical methods, the lack of careful observation and optimization can lead to misinterpretation of the data. In this Perspective, we highlight some commonly overlooked considerations in kinetic studies based on our experiences and present a general guide to proper optimization of reactions and analytics prior to acquiring kinetic data.

Carbon-substituted isocyanates and isothiocyanates are common building blocks in organic synthesis. In contrast, synthetic uses of N-substituted isocyanates and isothiocyanates are severely underdeveloped: few have been reported and their reactivity had not been compared. Herein, we compare the reactivity of blocked (masked) N-isocyanate and N-isothiocyanate precursors in cascade reactions. Divergent reactivity is observed with secondary propargylic and allylic systems, leading to new syntheses of imidazolones, thiazolidines, and a tool to form complex azomethine imines.

Cascade reactions for the synthesis of 1,2,4-triazinones and 5-aminopyridazinones are reported using α-ketocarbazones as N-isocyanate precursors and exploiting the divergent reactivity observed with primary and secondary amines. Triazinones were formed with primary amines, likely through addition of the amine on the N-isocyanate, followed by cyclization (condensation) on the ketone. In contrast, such cyclization is impossible for secondary amines; this allows in situ formation of enamines, which, upon cyclization, generate 5-amino pyridazinones. This sequence further illustrates the versatility of N-isocyanates in heterocyclic synthesis and provides a rare example of carbon nucleophiles reacting with N-isocyanates.