Selective Heck reaction of aryl bromides with cyclopent-2-en-1-one or cyclohex-2-en-1-one

A Synthesis of α-Alkyl Cycloenones by Pd-Catalyzed Suzuki-Miyaura Coupling with Cyclic Morita-Baylis-Hillman Adducts

We herein disclose a Pd-catalyzed Suzuki-Miyaura coupling of cyclic Morita-Baylis-Hillman adducts with organoboronic acids under mild conditions, which allows for a rapid access to diverse α-alkyl substituted cycloenones. The advantage of this method resides in the employment of functionalized allyl alcohols as the unprecedented electrophilic partners in the absence of external activators.

Controlling Reactivity and Selectivity in the Mizoroki-Heck Reaction: High Throughput Evaluation of 1,5-Diaza-3,7-diphosphacyclooctane Ligands

We report a high throughput evaluation of the Mizoroki-Heck reaction of diverse olefin coupling partners. Comparison of different ligands revealed the 1,5-diaza-3,7-diphosphacyclooctane (P2N2) scaffold to be more broadly applicable than common "gold standard" ligands, demonstrating that this family of readily accessible diphosphines has unrecognized potential in organic synthesis. In particular, two structurally related P2N2 ligands were identified to enable the regiodivergent arylation of styrenes. By simply altering the phosphorus substituent from a phenyl to tert-butyl group, both the linear and branched Mizoroki-Heck products can be obtained in high regioisomeric ratios. Experimental and computational mechanistic studies were performed to further probe the origin of selectivity, which suggests that both ligands coordinate to the metal in a similar manner but that rigid positioning of the phosphorus substituent forces contact with the incoming olefin in a π-π interaction (for P-Ph ligands) or with steric clash (for P-tBu ligands), dictating the regiocontrol.

Examining the Scope of Deriving β-Aryl Enones from Enol Silanes as Ketone Equivalents via Pd(II)-Mediated Sequential Dehydrosilylation and Arylation

Silyl enol ethers were examined as a masked source of saturated ketones to derive β-aryl enones and their derivatives by dehydrosilylation to generate enones in situ and subsequent oxidative arylation with arylboronic acids as transmetallation coupling partners using relayed Pd(II) catalysis in one pot under base-free conditions. Oxygen was found to be an efficient and green oxidant to enable both dehydrosilylation of enol silanes and arylation. Additionally, arylation conditions can be custom-designed to take advantage of aryl halides as an alternative source of arylating agents. The preparative scope was investigated with 35 examples (up to 95% yield), and mechanistic studies implied a cationic Pd(II)-based catalytic system.

Synthesis of 2,3,4-Trisubstituted 2-Cyclopentenones via Sequential Functionalization of 2-Cyclopentenone

The synthesis of differently substituted 2,3,4-triarylcyclopent-2-en-1-ones from 2-cyclopentenone via sequential functionalization of a novel 2,4-dibromo-3-(4-methoxyphenyl) cyclopent-2-en-1-one intermediate has been developed. The process provides access to selective arylation at C-4 and C-2 with a broader substrates scope, which includes heteroaryl and alkyl substitution at C-2.

Palladium-Catalyzed Regioselective Coupling Cyclohexenone into Indoles: Atom-Economic Synthesis of β-Indolyl Cyclohexenones and Derivatization Applications

Herein, we report a palladium-catalyzed dehydrogenative cross-coupling of indoles with cyclic enones to give β-indolyl cyclic enones under mild and neutral reaction conditions. The key to the success is to explore a mild condition, which ensures the indole C-H activation and subsequent syn β-hydride elimination through rapid enolization isomerization of Pd(II)-enolate while suppressing other undesired side reactions. Synthetic utility has also been demonstrated in the flexible transformation of the coupling products to meta-phenols and benzo[a]carbazoles.

Palladium-catalyzed dehydrogenative coupling of cyclic enones with thiophenes: a rapid access to β-heteroarylated cyclic enones

A dehydrogenative coupling reaction of cyclic enones with thiophenes through palladium-catalyzed C–H functionalization is reported herein. Further molecular transformations of the coupling products to synthetically useful meta-heteroarylated phenols are also demonstrated.

Catalytic dehydrogenative aromatization of cyclohexanones and cyclohexenones

Prompted by the scant attention paid by published literature reviews to the comprehensive catalytic dehydrogenative aromatization of cyclohexa(e)nones, this review describes recent methods developed to-date involving transition-metal-catalyzed oxidative aromatization and metal-free strategies for the transformation of cyclohexa(e)nones to substituted phenols.

Nickel-catalyzed cross-coupling of β-carbonyl alkenyl pivalates with arylzinc chlorides

The reaction of β-carbonyl alkenyl pivalates with arylzinc reagents was carried out via nickel-catalyzed C–O bond cleavage, forming 3-aryl-substituted α,β-unsaturated carbonyl compounds in moderate to excellent yields.

Enantioselective oxidative boron Heck reactions

This review highlights the use of the oxidative boron Heck reaction in enantioselective Heck-type couplings.

Oxidative Heck desymmetrisation of 2,2-disubstituted cyclopentene-1,3-diones

Oxidative Heck couplings have been successfully developed for 2,2-disubstituted cyclopentene-1,3-diones. The direct coupling onto the 2,2-disubstituted cyclopentene-1,3-dione core provides a novel, expedient and useful way of desymmetrising all-carbon quaternary centres.

Ligand- and base-free Pd(II)-catalyzed controlled switching between oxidative Heck and conjugate addition reactions

A simple change of solvent allows controlled and efficient switching between oxidative Heck and conjugate addition reactions on cyclic Michael acceptor substrates, catalyzed by a cationic Pd(II) catalyst system. Both reactions are ligand- and base-free and tolerant of air and moisture, and the controlled switching sheds light on some of the factors which favor one reaction over the other.

Aerobic oxidative Heck/dehydrogenation reactions of cyclohexenones: efficient access to meta-substituted phenols

A new dicationic PdII catalyst, employing a 6,6'-dimethylbipyridine ligand, has been identified that is capable of promoting both aerobic oxidative Heck coupling and dehydrogenation reactions of cyclohexenones. These reactions may be combined in a one-pot sequence to enable the straightforward synthesis of meta -substituted phenols.

Pd-NHC catalyzed conjugate addition versus the Mizoroki-Heck reaction

Ace of base: A catalytic system is presented that, solely by choice of the base, selectively switches between conjugate addition and the Mizoroki-Heck reaction of aryl halides with Michael acceptors (see scheme; R, R' = alkyl, aryl). For conjugate addition reactions, this avoids the preparation and use of organometallics.