Rapid and Modular Access to Vinyl Cyclopropanes Enabled by Air-stable Palladium(I) Dimer Catalysis

While vinyl cyclopropanes are valuable functional groups in drugs or natural products as well as established precursors to trigger a rich variety of synthetic transformations, their reactive nature can make their installation via direct catalytic approaches challenging. We herein present a modular access to (di)vinyl cyclopropanes under very mild conditions and full conservation of stereochemistry, allowing access to the cis or trans cyclopropane- as well as E or Z vinyl-stereochemical relationships. Our protocol relies on air-stable dinuclear Pd^I catalysis, which enables rapid (<30 min) and selective access to a diverse range of vinyl cyclopropane motifs at room temperature, even on gram scale.

Coupling of Reformatsky Reagents with Aryl Chlorides Enabled by Ylide-Functionalized Phosphine Ligands

The coupling of aryl chlorides with Reformatsky reagents is a desirable strategy for the construction of α‐aryl esters but has so far been substantially limited in the substrate scope due to many challenges posed by various possible side reactions. This limitation has now been overcome by the tailoring of ylide‐functionalized phosphines to fit the requirements of Negishi couplings. Record‐setting activities were achieved in palladium‐catalyzed arylations of organozinc reagents with aryl electrophiles using a cyclohexyl‐YPhos ligand bearing an ortho‐tolyl‐substituent in the backbone. This highly electron‐rich, bulky ligand enables the use of aryl chlorides in room temperature couplings of Reformatsky reagents. The reaction scope covers diversely functionalized arylacetic and arylpropionic acid derivatives. Aryl bromides and chlorides can be converted selectively over triflate electrophiles, which permits consecutive coupling strategies.

Efficient Pd-Catalyzed Direct Coupling of Aryl Chlorides with Alkyllithium Reagents

Organolithium compounds are amongst the most important organometallic reagents and frequently used in difficult metallation reactions. However, their direct use in the formation of C-C bonds is less established. Although remarkable advances in the coupling of aryllithium compounds have been achieved, Csp2 -Csp3 coupling reactions are very limited. Herein, we report the first general protocol for the coupling or aryl chlorides with alkyllithium reagents. Palladium catalysts based on ylide-substituted phosphines (YPhos) were found to be excellently suited for this transformation giving high selectivities at room temperature with a variety of aryl chlorides without the need for an additional transmetallation reagent. This is demonstrated in gram-scale synthesis including building blocks for materials chemistry and pharmaceutical industry. Furthermore, the direct coupling of aryllithiums as well as Grignard reagents with aryl chlorides was also easily accomplished at room temperature.

Site-Selective, Modular Diversification of Polyhalogenated Aryl Fluorosulfates (ArOSO2 F) Enabled by an Air-Stable PdI Dimer

Since 2014, the interest in aryl fluorosulfates (ArOSO2 F) as well as their implementation in powerful applications has continuously grown. In this context, the enabling capability of ArOSO2 F will strongly depend on the substitution pattern of the arene, which ultimately dictates its overall function as drug candidate, material, or bio-linker. This report showcases the modular, substrate-independent, and fully predictable, selective functionalization of polysubstituted arenes bearing C-OSO2 F, C-Br, and C-Cl sites, which makes it possible to diversify the arene in the presence of OSO2 F or utilize OSO2 F as a triflate surrogate. Sequential and triply selective arylations and alkylations were realized within minutes at room temperature, using a single and air-stable PdI dimer.

Murahashi Cross-Coupling at -78 °C: A One-Pot Procedure for Sequential C-C/C-C, C-C/C-N, and C-C/C-S Cross-Coupling of Bromo-Chloro-Arenes

The coupling of organolithium reagents, including strongly hindered examples, at cryogenic temperatures (as low as -78 °C) has been achieved with high-reactivity Pd-NHC catalysts. A temperature-dependent chemoselectivity trigger has been developed for the selective coupling of aryl bromides in the presence of chlorides. Building on this, a one-pot, sequential coupling strategy is presented for the rapid construction of advanced building blocks. Importantly, one-shot addition of alkyllithium compounds to Pd cross-coupling reactions has been achieved, eliminating the need for slow addition by syringe pump.

One-Pot Sequential Kumada-Tamao-Corriu Couplings of (Hetero)Aryl Polyhalides in the Presence of Grignard-Sensitive Functional Groups Using Pd-PEPPSI-IPentCl

We report a general and rapid chemoselective Kumada-Tamao-Corriu (KTC) cross-coupling of aryl bromides in the presence of chlorides or triflates with functionalized Grignard reagents at 0 °C in 15 min by using Pd-PEPPSI-IPent^Cl (C4). Nucleophiles and electrophiles (or both) can contain Grignard-sensitive functional groups (-CN, -COOR, etc.). Control experiments together with DFT calculations suggest that transmetallation is rate limiting for the selective cross-coupling of Br in the presence of Cl/OTf with functionalized Grignard reagents. One-pot sequential KTC/KTC cross-couplings with bromo-chloro arenes have been demonstrated for the first time. We also report the one-pot sequential KTC/Negishi cross-couplings using C4 showcasing the versatility of this methodology.

Barbier-Negishi Coupling of Secondary Alkyl Bromides with Aryl and Alkenyl Triflates and Nonaflates

A mild and practical Barbier-Negishi coupling of secondary alkyl bromides with aryl and alkenyl triflates and nonaflates has been developed. This challenging reaction was enabled by the use of a very bulky imidazole-based phosphine ligand, which resulted in good yields as well as good chemo- and site selectivities for a broad range of substrates at room temperature and under non-aqueous conditions. This reaction was extended to primary alkyl bromides by using an analogous pyrazole-based ligand.

Palladium(I) Dimer Enabled Extremely Rapid and Chemoselective Alkylation of Aryl Bromides over Triflates and Chlorides in Air

Disclosed herein is the first general chemo- and site-selective alkylation of C-Br bonds in the presence of COTf, C-Cl and other potentially reactive functional groups, using the air-, moisture-, and thermally stable dinuclear PdI catalyst, [Pd(μ-I)PtBu3 ]2 . The bromo-selectivity is independent of the substrate and the relative positioning of the competing reaction sites, and as such fully predictable. Primary and secondary alkyl chains were introduced with extremely high speed (<5 min reaction time) at room temperature and under open-flask reaction conditions.

Improved reactivity of a cyclic 13/15 compound by increased steric demand

The reactivity of a masked flp was investigated for the sterically overloaded group 13/15 ring compound [tBu₂GaP(H)tBu₂Ph]₂, as can be seen from its reaction with phenyl-isocyanate.

Ligand-Promoted C(sp(3) )-H Olefination en Route to Multi-functionalized Pyrazoles

A Pd-catalyzed/N-heterocycle-directed C(sp(3) )-H olefination has been developed. The monoprotected amino acid ligand (MPAA) is found to significantly promote Pd-catalyzed C(sp(3) )-H olefination for the first time. Cu(OAc)2 instead of Ag(+) salts are used as the terminal oxidant. This reaction provides a useful method for the synthesis of alkylated pyrazoles.

Enantioconvergent Fukuyama Cross-Coupling of Racemic Benzylic Organozinc Reagents

The first enantioconvergent palladium-catalyzed Fukuyama cross-coupling of racemic benzylic organozinc reagents with thioesters has been developed. The reaction furnishes enantioenriched acyclic α-disubstituted ketone products in good yields and high enantioselectivities. A broad substrate scope is achieved under mild reaction conditions to prevent racemization of the potentially labile tertiary stereocenters.

Room-temperature amination of deactivated aniline and aryl halide partners with carbonate base using a Pd-PEPPSI-IPentCl-o-picoline catalyst

Current state-of-the-art protocols for the coupling of unreactive amines (e.g., electron-poor anilines) with deactivated oxidative-addition partners (e.g., electron-rich and/or hindered aryl chlorides) involve strong heating (usually >100°C) and/or tert-butoxide base, and even then not all couplings are successful. The aggressive base tert-butoxide reacts with and in many instances destroys the typical functional groups that are necessary for the function of most organic molecules, such as carbonyl groups, esters, nitriles, amides, alcohols, and amines. The new catalyst described herein, Pd-PEPPSI-IPentCl-o-picoline, is able to aminate profoundly deactivated coupling partners when using only carbonate base at room temperature.

Cobalt-catalyzed cross-coupling of 3- and 4-iodopiperidines with Grignard reagents

A cobalt-catalyzed cross-coupling between 3- and 4-iodopiperidines and Grignard reagents is disclosed. The reaction is an efficient, cheap, chemoselective, and flexible way to functionalize piperidines. This coupling was used as the key step to realize a short synthesis of (±)-preclamol. Some mechanistic investigations were conducted that highlight the formation of radical intermediates.