Chemoselective methoxycarbonylation of terminal alkynes catalyzed by Pd(ii)-TROPP complexes

Assembly of 5H-dibenzo[a,d]cycloheptenes by a formal [5 + 2] annulation of ortho-aryl alkynyl benzyl alcohols with arenes

A new synthetic methodology for the synthesis of 5H-dibenzo[a,d]cycloheptenes from ortho-aryl alkynyl benzyl alcohols and arenes via a Tf₂O-mediated formal [5 + 2] annulation reaction has been achieved. From this transformation, structurally diverse 5H-dibenzo[a,d]cycloheptenes were achieved in moderate to good yields. This transformation probably involves an intermolecular Friedel-Crafts-type alkylation and a subsequent intramolecular 7-endo-dig cyclization in one pot, highlighting the high efficiency, regioselectivity, and step-economy of this protocol.

Low-valent homobimetallic Rh complexes: influence of ligands on the structure and the intramolecular reactivity of Rh-H intermediates

Supporting two metal binding sites by a tailored polydentate trop-based (trop = 5H-dibenzo[a,d]cyclohepten-5-yl) ligand yields highly unsymmetric homobimetallic rhodium(i) complexes. These were studied as models for Rh/C hydrogenation catalysts.

Supporting two metal binding sites by a tailored polydentate trop-based (trop = 5H-dibenzo[a,d]cyclohepten-5-yl) ligand yields highly unsymmetric homobimetallic rhodium(i) complexes. Their reaction with hydrogen rapidly forms Rh hydrides that undergo an intramolecular semihydrogenation of two C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> C bonds of the trop ligand. This reaction is chemoselective and converts C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> C bonds to a bridging carbene and an olefinic ligand in the first and the second semihydrogenation steps, respectively. Stabilization by a bridging diphosphine ligand allows characterization of a Rh hydride species by advanced NMR techniques and may provide insight into possible elementary steps of H₂ activation by interfacial sites of heterogeneous Rh/C catalysts.

2-Pyridyl substituents enhance the activity of palladium-phospha-adamantane catalysts for the methoxycarbonylation of phenylacetylene

The synthesis of a series of CgPAr ligands is reported, where CgP is the 6-phospha-2,4,8-trioxa-1,3,5,7-tetramethyladamant-6-yl moiety and Ar = 2-pyridyl (L2), 3-pyridyl (L3), 2-pyrimidyl (L4), 4-R-2-pyridyl [R = Me (L5a), CF₃ (L6a), SiMe₃ (L7a)] or 6-R-2-pyridyl [R = Me (L5b), CF₃ (L6b), SiMe₃ (L7b). Testing of these ligands in the Pd-catalysed methoxycarbonylation of phenylacetylene reveals that the activity and branched selectivity of the catalysts derived from these ligands varies as a function of the N-heterocycle, with the catalyst derived from L5b being the most active of those tested. This, together with the poor performance of catalysts derived from L3 supports the hypothesis that the catalysis proceeds by a "proton shuttling" mechanism, an idea that previously had only been applied to arylphosphines. Reaction of [PtCl₂(cod)] with L where L = L2 or L4-7 yields a rac/meso mixture of the trans-[PtCl₂(L)₂] (1a-h) complexes, three of which are structurally characterised. ³¹P NMR spectroscopy shows that reaction of L3 with [PtCl₂(cod)] gives a mixture of mononuclear and binuclear metal complexes in solution. The complex trans-[PdCl₂(L2)₂] (4) reacts with AgBF₄ to give the [PdCl(κ¹-L2)(κ²-L2)]BF₄ (5) with spectroscopic and structural characterisation confirming the presence of a P,N-chelate. ¹H and ³¹P NMR evidence supports the assignment of a pyridyl-protonated species being formed upon treatment of 4 with TsOH·H₂O in CD₂Cl₂; both the protonated species and chelate 5 are observed when the reaction is carried out in MeOH.

One-pot synthesis of propynoates and propynenitriles

An efficient transformation towards propynoates and propynenitriles is herein described. The practical methodology was conducted at low temperature (–78 or –60 °C) in a one-pot manner with the assistance of base rather than any transition metal catalysts. The base-induced protocol exhibits good functional group tolerance (up to 28 examples) and high efficiency (up to 92% yields) towards substituted acetylenes of great synthetic significance, which was also well demonstrated by the gram-scale reactions.