The first copper‐catalyzed enantioselective allylboration of alkynes is reported. The method employs a multitasking chiral NHC‐Cu catalyst and provides access to densely functionalized molecules from ...simple starting materials with excellent levels of chemo‐, regio‐, and enantioselectivity. These multifunctional products display highly versatile reactivity as shown by the synthesis of a variety of non‐racemic molecular scaffolds. DFT calculations were conducted to gain insight into the high selectivity levels of this catalytic process.
Complexity from simplicity: A copper‐catalyzed enantioselective alkyne allylboration provides access to non‐racemic densely functionalized molecules from simple starting materials with remarkable chemo‐, regio‐, and enantioselectivity. These multifunctional products are easily converted into a variety of important molecular scaffolds.
A novel class of N-doped cationic PAHs (polycyclic aromatic hydrocarbons) bearing the benzoc,dfluoranthene scaffold has been synthesized by the Rh(III)-catalyzed double-oxidative annulation of ...2-arylbenzimidazoles with alkynes. The overall process involves a double C–N bond formation through a double C–H/N–H functionalization.The solid-state structures and electronic properties of the new N-doped PAHs were analyzed. These cationic azapolycycles were readily reduced in the presence of LiAlH4 or by the addition of PhLi to give interesting phenyl and diphenylmethanediamine derivatives.
RhIII-catalyzed tandem C–H allylation and oxidative cyclization of anilides with allyl carbonates in the presence of a slight excess of AgSbF6 salt and Cu(OAc)2 as oxidant affords easy, economical ...access to important bioactive 2-methylindoles. The new reaction supports a wide range of functional groups on the anilide substrate. A possible mechanism is proposed as a basis for its rational further development.
A novel synthesis of 2‐vinyldihydropyrans and dihydro‐1,4‐oxazines (morpholine derivatives) from alkynals and alkynones has been developed. The cyclizations require a mild generation of catalytic ...ruthenium carbenes from terminal alkynes and (trimethylsilyl)diazomethane followed by trapping with carbonyl nucleophiles. Mechanistic aspects of the new cyclizations are discussed.
Setting a trap: A novel synthesis of 2‐vinyldihydropyrans and dihydro‐1,4‐oxazines (morpholine derivatives) from alkynals and alkynones has been developed. The cyclizations require a mild generation of catalytic ruthenium carbenes from terminal alkynes and (trimethylsilyl)diazomethane followed by trapping with carbonyl nucleophiles.
Ru-catalyzed cycloisomerizations of aromatic homo- and bis-homopropargylic alcohols effectively afford benzofurans and isochromenes. These processes proved to be chemo- and regioselective (5-, and ...6-endo cyclizations) derived from key Ru vinylidene intermediates. The presence of an amine/ammonium base−acid pair is crucial for the catalytic cycle.
Complex CpRuCl(PPh3)2 catalyzes reactions of terminal alkynes with 4-picoline N-oxide and primary and secondary amines to afford the corresponding amides. The reactions occur in chlorinated solvent ...and aqueous medium, showing applications in peptide chemistry. Stoichiometric studies reveal that the true catalysts of the processes are the vinylidene cations CpRu(CCHR)(PPh3)2+ which are oxidized to the Ru(η2-CO)-ketenes by the N-oxide. Finally, nucleophilic additions of primary and secondary amines to the free ketenes yield the corresponding amides.
Benzofused seven-membered heterocycles such as 1,4-benzoediazepines (1,4-BZDs) and 1,4-benzoeoxazepines (1,4-BZOs) were efficiently synthesized by Rh-catalyzed hydrofunctionalization of internal ...alkynes and allenes in good to excellent yields. The asymmetric hydroamination of (aminomethyl)anilines gave rise to 3-vinyl-1,4-BZDs with excellent enantioselectivities. Orthogonal N-deprotection of 1,4-BZDs allowed an easy entry to an advanced pyrrolobenzodiazepine metabolite of the V2-receptor antagonist Lixivaptan.
A new ruthenium‐catalyzed cyclization of ortho‐(alkynyloxy)benzylamines to dihydro‐1,3‐benzoxazines is reported. The cyclization is thought to take place via the vinyl ruthenium carbene intermediates ...which are easily formed from Cp*RuCl(cod) and N2CHSiMe3. The mild reaction conditions and the efficiency of the procedure allow the easy preparation of a broad range of new 2‐vinyl‐2‐substituted 1,3‐benzoxazine derivatives. Rearrangement of an internal C(sp) in the starting material into a tetrasubstituted C(sp3) atom in the final 1,3‐benzoxazine is highly remarkable.
A new addition: A new ruthenium‐catalyzed cyclization of ortho‐(alkynyloxy)benzylamines to 1,3‐benzoxazines is reported. Vinyl ruthenium carbenes are proposed as the key intermediates, and the mechanistic hypothesis supposes the first example of a nucleophilic addition of amines to vinyl ruthenium carbenes. Rearrangement of an internal C(sp) into a tetrasubstituted C(sp3) is highly remarkable. TMS=trimethylsilyl.
A novel tandem Ru-catalyzed 2+2+2 cycloaddition of arylenynes to dihydrobiphenylenes followed by halogen-radical ring opening has been developed for the construction of tub-shaped halogenated ...benzocyclooctatetraenes (bCOT’s). Cross-couplings and Diels–Alder reactions of the brominated bCOT’s allow the formation of the corresponding eight-membered ring-fused PAH’s. The halogen-radical ring opening probably occurs via a selective formation of a bis-allyl radical at the 1,3-cyclohexadiene moiety, halogenation at the bridgehead carbon, and finally electrocyclic ring opening.
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