Crystal structure of an uncomplexed 25-crown-7 comprising one 2,6-pyridino and two 1,4-benzo condensations

Single crystal X-ray analysis of the uncomplexed crown macroring 1 is reported. Crystals are triclinic, , witha=10.809(1),b=10.945(1),c=10.256(1) Å, =107.85(1), =104.15(1), =87.27(1)°,D _c=1.318 g cm^–3,Z=2. Three torsion angles in the macrocycle take upgauche conformations in contrast to the usualanti conformation. The crystal structure is stabilized by intramolecular van der Waals forces and weak C–H...O and C–H...N hydrogen bond attractions. Stacking of pyridine rings is a noticeable packing feature in the crystal lattice. Supplementary Data relating to this article are deposited with the British Library as Supplementary Publication No. SUP 82168 (6 pages).Macroring Uncharged Molecule Complexation. Part 20. For Part 19 of this series see Ref. [1].     

Solid state structure of the hydrated potassium thiocyanate complex of benzodinaphthopyridino 21-crown-7, C37H31NO6·KSCN·H2O (1 : 1 : 1)

Single crystal X-ray analysis of the hydrated KSCN complex of benzodinaphthopyridino-21-crown-7 (1) (1 : 1 : 1) is reported. Crystals of the complex are orthorhombic,Pnma, with = 16.946(4),b = 22.298(4),c = 10.390(8) Å andD _c = 1.184 g cm^–1,Z = 4. The host macroring (1) has a mirror symmetry and exists in a so-called dentists chair conformation. The cation (K^–) is coordinated to all the six ether oxygen atoms and also weakly to the pyridine N atom. The SCN^– anion group has a statistical type of disorder with opposite orientations of S and N such that nitrogen and sulphur are coordinated to K⁺. Packing of the host molecules is in columns to form quasi channels with K⁺, SCN^–, and H₂O being located inside the stacks. Supplementary Data relating to this article are deposited with the British Library as Supplementary Publication No. SUP 82132 (9 pages).     

Nickel‐Catalyzed Mizoroki–Heck‐ versus Michael‐Type Addition of Organoboronic Acids to α,β‐Unsaturated Alkenes through Fine‐Tuning of Ligands

Various arylboronic acids reacted with activated alkenes in the presence of [Ni(dppe)Br₂], ZnCl₂, and H₂O in CH₃CN at 80 °C to give the corresponding Mizoroki–Heck‐type addition products in good to excellent yields. Furthermore, 1 equivalent of the hydrogenation product of the activated alkene was also produced. By tuning the ligands of the nickel complexes and the reaction conditions, Michael‐type addition was achieved in a very selective manner. Thus, various p‐ and o‐substituted arylboronic acids or alkenylboronic acid reacted smoothly with activated alkenes in CH₃CN at 80 °C for 12 h catalyzed by Ni(acac)₂, P(o‐anisyl)₃, and K₂CO₃ to give the corresponding Michael‐type addition products in excellent yields. However, for m‐substituted arylboronic acids, the yields of Michael‐type addition products are very low. The cause of this unusual meta‐substitution effect is not clear. By altering the solvent or phosphine ligand, the product yields for m‐substituted arylboronic acids were greatly improved. In contrast to previous results in the literature, the present catalytic reactions required water for Mizoroki–Heck‐type products and dry reaction conditions for Michael‐type addition products. Possible mechanistic pathways for both addition reactions are proposed.     

Rhodium-catalyzed one-pot synthesis of substituted pyridine derivatives from alpha,beta-unsaturated ketoximes and alkynes

A rhodium-catalyzed chelation-assisted C-H activation of alpha,beta-unsaturated ketoximes and the reaction with alkynes to afford highly substituted pyridine derivatives is described.     

Transition metal-catalyzed three-component coupling of allenes and the related allylation reactions

The feature article surveys the transition metal-catalyzed three-component coupling of allenes and the related allylation reactions. Most of the reactions shown in the article mechanistically proceed via oxidative addition of organic electrophiles to metals, followed by carbometallation of allene and then transmetalation by main group metals or reagents and organometallic reagents. These reactions provide an efficient route for the synthesis of various substituted allyl and vinyl metal reagents and complex organic molecules in highly regio-, stereo- and chemoselective manner in one pot. The metal reagents or pi-allyl-metal intermediates obtained from the reaction are utilized for the allylation of aldehydes, ketones and imines, producing various homoallylic alcohols and amines in a highly regio- and stereoselective manner.     

Copper-catalyzed three-component coupling of arynes, terminal alkynes and activated alkenes

The three-component coupling of benzynes with terminal alkynes and activated alkenes in the presence of CuI, PCy(3) and CsF in a 1:1 mixture of CH(3)CN and THF at 50 degrees C for 5 h gave 1-alkyl-2-alkynylbenzenes in good to moderate yields.     

Cobalt-catalyzed intramolecular [2 + 2 + 2] cocyclotrimerization of nitrilediynes: an efficient route to tetra- and pentacyclic pyridine derivatives

[reaction: see text] In this paper, we wish to report the intramolecular [2 + 2 + 2] cocyclotrimerization of nitrilediynes catalyzed by the CoI2(dppe)/Zn system at 80 degrees C in CH3CN. Under these reaction conditions, various highly substituted nitrilediynes having steric conjunction at the alpha and beta positions to a nitrile group and a bulkier substitution at the terminal carbon of alkyne undergo [2 + 2 + 2] cocylotrimerization to afford tetra- and pentacyclic pyridine derivatives in good to excellent yields.     

Platinum‐Catalyzed Multi‐Step Reaction of Propargyl Alcohols with N‐Heteroaromatics

N‐Methyl indole reacts with but‐2‐yn‐1‐ol in the presence of PtCl₂ in MeOH giving indole derivatives having a substituted 3‐oxobutyl group at the 3‐position in good yield. Under the reaction conditions, various substituted indoles and substituted propargyl alcohols are successfully involved in the reaction giving the corresponding addition products in good to moderate yields. The catalytic reaction can be further extended to N‐phenyl pyrrole. In the present multi‐step reaction, PtCl₂ likely plays dual roles: as the catalyst for the rearrangement of propargyl alcohols to the corresponding alkenyl ketones and as the catalyst for the addition of indoles to the alkenyl ketones. Experimental evidence is provided to support the proposed mechanism.     

Ruthenium-catalyzed regioselective oxidative coupling of aromatic and heteroaromatic esters with alkenes under an open atmosphere

A ruthenium-catalyzed oxidative coupling of substituted aromatic and heteroaromatic esters with alkenes in the presence of catalytic amounts of AgSbF(6) and Cu(OAc)(2) to provide highly substituted alkene derivatives in good to excellent yields under an open atmosphere is described.