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.

Preparation and X-Ray Structure of [YbIII(η5-C5H5)2(OPPh3)(OPPh2C5H4)]—a Complex With Oxygen Rather Than Cyclopentadienide Coordination of a Novel Ambidentate Ligand

The structure (9) of the title compound, obtained by treatment of the mother liquor from recrystallization of the naturally occurring acid (6a) with 4-phenyl-1,2,4-triazoline-3,5-dione, has been elucidated by X-ray crystallographic analysis.

Constituents of Endiandra species. V. 2-[3',5'-Dioxo-4'-phenyl-10'-{(E,E)-5''-phenyl-penta-2'',4''-dien-1''-yl}-2',4',6'-triazatetracyclo[5,4,2,02,6,08,11]tridec12'-en-9'-yl]-acetic acid derived from Endiandra introrsa (Lauraceae)

The compound [Cr2(CO)6(AsMe)9] contains a nine-membered As ring co-ordinated to each Cr atom through three As atoms while [Mo2(CO)6(AsPrn)8] contains a chain of eight As atoms with terminal As atoms bridging both metal atoms and one other arsenic atom in the chain also co-ordinated to each metal, together with an Mo–Mo bond.

X-Ray structures of [Cr2(CO)6(AsMe)9] and [Mo2(CO)6(AsPrn)8]: the stabilisation of an As9 ring and an As8 chain by co-ordination

Isopropylideneketene (3-methylbuta-1,2-dien-1-one), Me2C=C=C=O, reacts with ketene and substituted ketenes to give oxetanones or cyclobutane-1,3-diones formed by [2+2] cycloadditions involving the central C=C bond of the methyleneketene. By contrast Me2C=C=C=O reacts with 5,5- dimethylpyrroline 1-oxide to give a spirooxazolidinone (13) and an oxetanone (17), both of which appear to be formed by initial cycloaddition of the pyrroline 1-oxide to the terminal C=C bond of the methyleneketene and formation of an intermediate bicyclic ketene (15). The structure of the oxetanone (17) has been confirmed and its stereochemistry established by X-ray crystallography.

Methyleneketenes and methylenecarbenes. XIII. Cycloaddition of ketenes and of a 1-pyrroline 1-oxide to isopropylideneketene

The title compound crystallizes in space group P21/c with a= 6·429(6), b= 13·619(14), c= 10·047(10)A, β= 107·88(1)°, Z= 2. The structure has been determined by Patterson and Fourier methods and refined to R 0·057 from three-dimensional diffractometer data (1325 observed reflections). Its structure consists of discrete monomeric units which are required crystallographically to be centrosymmetric. The two chlorine atoms are in a trans arrangement and the bond distances Mo–Cl, Mo–O, and Mo–N are respectively 2·39, 1·95, and 2·14 A.

Bryan M. Gatehouse

Papers

Preparation and X-Ray Structure of [YbIII(η5-C5H5)2(OPPh3)(OPPh2C5H4)]—a Complex With Oxygen Rather Than Cyclopentadienide Coordination of a Novel Ambidentate Ligand

Constituents of Endiandra species. V. 2-[3',5'-Dioxo-4'-phenyl-10'-{(E,E)-5''-phenyl-penta-2'',4''-dien-1''-yl}-2',4',6'-triazatetracyclo[5,4,2,02,6,08,11]tridec12'-en-9'-yl]-acetic acid derived from Endiandra introrsa (Lauraceae)

X-Ray structures of [Cr2(CO)6(AsMe)9] and [Mo2(CO)6(AsPrn)8]: the stabilisation of an As9 ring and an As8 chain by co-ordination

Methyleneketenes and methylenecarbenes. XIII. Cycloaddition of ketenes and of a 1-pyrroline 1-oxide to isopropylideneketene

Crystal and molecular structure of trans-dichlorobis-(N-methylsalicylaldiminato)molybdenum(IV)