Relationships between the carbon-oxygen stretching frequencies of carboxylato complexes and the type of carboxylate coordination

In studying the evolution of organic chemistry and grasping its essence, one comes quickly to the conclusion that no other type of reaction plays as large a role in shaping this domain of science than carbon-carbon bond-forming reactions. The Grignard, Diels-Alder, and Wittig reactions are but three prominent examples of such processes, and are among those which have undeniably exercised decisive roles in the last century in the emergence of chemical synthesis as we know it today. In the last quarter of the 20th century, a new family of carbon-carbon bond-forming reactions based on transition-metal catalysts evolved as powerful tools in synthesis. Among them, the palladium-catalyzed cross-coupling reactions are the most prominent. In this Review, highlights of a number of selected syntheses are discussed. The examples chosen demonstrate the enormous power of these processes in the art of total synthesis and underscore their future potential in chemical synthesis.

Palladium-catalyzed cross-coupling reactions in total synthesis.

Sol-gel chemistry of transition metal oxides

The design and implementation of cascade reactions is a challenging facet of organic chemistry, yet one that can impart striking novelty, elegance, and efficiency to synthetic strategies. The application of cascade reactions to natural products synthesis represents a particularly demanding task, but the results can be both stunning and instructive. This Review highlights selected examples of cascade reactions in total synthesis, with particular emphasis on recent applications therein. The examples discussed herein illustrate the power of these processes in the construction of complex molecules and underscore their future potential in chemical synthesis.

Cascade reactions in total synthesis.

The Diels-Alder reaction has both enabled and shaped the art and science of total synthesis over the last few decades to an extent which, arguably, has yet to be eclipsed by any other transformation in the current synthetic repertoire. With myriad applications of this magnificent pericyclic reaction, often as a crucial element in elegant and programmed cascade sequences facilitating complex molecule construction, the Diels-Alder cycloaddition has afforded numerous and unparalleled solutions to a diverse range of synthetic puzzles provided by nature in the form of natural products. In celebration of the 100th anniversary of Alder's birth, selected examples of the awesome power of the reaction he helped to discover are discussed in this review in the context of total synthesis to illustrate its overall versatility and underscore its vast potential which has yet to be fully realized.

https://www.ch.ic.ac.uk/local/organic/pericyclic/DA.pdf

The Diels--Alder reaction in total synthesis.

2-(Pyridin-2'-yl) phenylmercuric acetate has been prepared by mercuration of 2-phenylpyridine. Symmetrization of the corresponding chloride by alkaline sodium stannite gave bis [2-(pyridin-2'-yl)phenyl]mercury, which was also prepared from 2-(2'-aminophenyl)pyridine by the diazo method and treatment of the initial product with copper powder and aqueous ammonia. Mercuration of benzo [h] quinoline and 3,4,5-trimethyl-1-phenylpyrazole with mercuric acetate followed by treatment with lithium chloride yielded benzo [h]quinolin-10-ylmercuric chloride and 2-(3',4',5'-trimethylpyrazol-1'-yl) phenylmercuric chloride respectively. Treatment of the former product with tribromide ions gave 10-bromobenzo[h] quinoline. The exchange Grignard reaction between 1-phenylpyrazole and ethylmagnesium bromide to give 2-(pyrazol-1'-yl) phenylmagnesium bromide has been monitored by reactions with benzonitrile and D2O to establish optimum conditions for reaction with mercuric bromide giving bis [2-(pyrazol-1'-yl)phenyl]mercury. The 199Hg n.m.r. chemical shifts of the majority of mercurials are shifted substantially downfield relative to the corresponding simple phenylmercurials consistent with weak intramolecular coordination by the heterocyclic nitrogen donor atoms, but a small upfield shift is observed for bis [2-(pyrazol-1'-yl)phenyl]mercury. The X-ray crystal structure of bis [2-(pyridin-2′-yl)phenyl]mercury [monoclinic, space group P21/n, a 12.746(2), b 11.660(2), c 5.698(1) Ǻ, β 92.81(1)′, V 845.8 Ǻ3] shows a centrosymmetric molecule with strong linear two coordination [Hg-C 2.098(8) Ǻ; C-Hg-C 180.0°] and significant but much weaker Hg-N interactions [Hg-N 2.798(7) Ǻ; N-Hg-N 180.0°] giving overall distorted square planar stereochemistry. The phenyl rings are mutually coplanar, whilst the two pyridin-2'-yl rings are parallel and inclined at 10.8° to the phenyl groups.

Organomercury Compounds. XXXI. Preparations and 199Hg N.M.R. Spectra of Organomercury Derivatives of 2-Phenylpyridine, Benzo[h]quinoline, 1-Phenylpyrazole and 3,4,5-Trimethyl-1-phenylpyrazole, and the X-Ray Crystal Structure of Bis[2-(pyridin-2'-yl)phenyl]mercury

Reaction of neodymium metal with bis ( pentafluorophenyl )mercury and pyrazole ( Hpz ) or 3,5-dimethylpyrazole ( Hdmpz ) in tetrahydrofuran ( thf ) yields Nd ( pz )3 or [ Nd ( dmpz )3( thf )]2. X-Ray crystallography has shown that [Nd (dmpz )3( thf )]2 [triclinic, space group Pī (No. 2), a 11.070(4), b 11.364(3), c 10.867(2)Ǻ, α 103.00(1), β 120.78(3), γ 97.68(2)°, R 0.0235, Rw 0.0247 for 5575 observed reflections] has a novel centrosymmetric dimeric structure. Each neodymium is eight-coordinate (4,4 bicapped trigonal prism) with two terminal chelating dmpz ligands [ Nd -N 2.400(2), 2.413(3), 2.422(3), 2.426(3)Ǻ], two bridging dmpz ligands [ Nd -N 2.509(2), 2.511(2)Ǻ], and, unexpectedly, two bridging tetrahydrofuran ligands [ Nd -O 2.792(2), 2.757(2)Ǻ].

Organoamido- and Aryloxo-lanthanoids. III. Preparation and X-Ray Structure of Bis(μ-3,5-dimethylpyrazolato-N:N′)bis(μ-tetrahydrofuran-O)-bis[bis(η2-3,5-dimethylpyrazolato-N,N')neodymium(III)]

Davidite from the Pandora Prospect, Pima County, Arizona, crystallizes in the space group R anti 3 with lattice parameters ..cap alpha.. = 9.190(3)A, ..cap alpha.. = 68.73(1)/sup 0/. Its formula, determined from microprobe analysis, is REE/sub 0/ /sub 91/U/sub 0/ /sub 33/Ca/sub 0/ /sub 20/Y/sub 0/ /sub 25/(Sr,Th,Pb)/sub 0/ /sub 09/Ti/sub 12/ /sub 53/Fe/sub 5/ /sub 97/Mg/sub 0/ /sub 24/Cr/sub 0/ /sub 21/Al/sub 0/ /sub 14/(Mn,V,Zr,Nb,Sc)/sub 0/ /sub 23/O/sub 38/. In its natural state the mineral is metamict. The crystal structure was reconstituted by heating in air at 920/sup 0/C for two hours. Davidite is isostructural with the crichtonite-group minerals, having a structure based on a close-packed anion lattice with a mixed stacking sequence (hhc...), and with rare-earth elements (REE, M(0), occupying a site in the anion framework. The U atom does not substitute for REE in M(0), but occupies an octahedral site M(1) along with Y and small REE. The remaining small metal atoms, mainly Ti and Fe, occupy a tetrahedral site. M(2), and three other octahedral sites, M(3), M(4), and M(5). A comparison is made of the site occupancies and average metal-oxygen bond lengths for five crichtonite-group minerals - senaite, crichtonite, davidite, loveringite, and landauite. A linear correlationmore » is observed between the unit-cell edge, a/sub rh/, and the M(1)-O bond length.« less

The crystal structure of davidite

The crystal structures of Ag2Mo2O7(I) and Ag2W2O7(II) have been determined by single-crystal X-ray analysis Both compounds crystallize in space group P, Z= 2, with for (I): a= 6095(3), b= 7501(3), c= 7681(3)A, α= 1104(1), β= 933(1), γ= 1135(1)°; and for (II): a = 6033(3), b= 7051 (3), c= 7735(3)A, α= 738(1), β= 922(1), γ= 1047(1)° The structures were determined from diffractometer data by heavy-atom methods and refined to R 0045 [(I), 1 208 observed reflections] and 0047 [(II), 1 364 observed reflections] The structures consist of infinite chains formed by blocks of four edge-shared octahedra joined by edge-sharing in (I), and by corner-sharing in (II), with the silver ions situated between the chains

Crystal structures of silver dimolybdate, Ag2Mo2O7, and silver ditungstate, Ag2W2O7

The structure (5) is proposed for the title compound on the basis of chemical and spectroscopic evidence and on the X-ray crystal structure of the derivative 4-{(Y-methyl-1'',3''-dioxo-7''-phenyl- 1'',3'',3'',4'',7'',7a''-hexahydroisoindol-4''-yl)methyl}tetracyclo [5,4,0,02,5,O3,9] undec-10-ene-8-carboxylic acid (9c).

Constituents of Endiandra species. III. 4-[(E,E)-5'-Phenylpenta-2',4'-dien-1'-yl]tetra-cyclo[5,4,0,02,5,03,9]undec-10-ene-8-carboxylic acid from Endiandra introrsa (Lauraceae)

Bryan M. Gatehouse

Papers

Organomercury Compounds. XXXI. Preparations and 199Hg N.M.R. Spectra of Organomercury Derivatives of 2-Phenylpyridine, Benzo[h]quinoline, 1-Phenylpyrazole and 3,4,5-Trimethyl-1-phenylpyrazole, and the X-Ray Crystal Structure of Bis[2-(pyridin-2'-yl)phenyl]mercury

Organoamido- and Aryloxo-lanthanoids. III. Preparation and X-Ray Structure of Bis(μ-3,5-dimethylpyrazolato-N:N′)bis(μ-tetrahydrofuran-O)-bis[bis(η2-3,5-dimethylpyrazolato-N,N')neodymium(III)]

The crystal structure of davidite

Crystal structures of silver dimolybdate, Ag2Mo2O7, and silver ditungstate, Ag2W2O7

Constituents of Endiandra species. III. 4-[(E,E)-5'-Phenylpenta-2',4'-dien-1'-yl]tetra-cyclo[5,4,0,02,5,03,9]undec-10-ene-8-carboxylic acid from Endiandra introrsa (Lauraceae)