R. B. Woodward

Conjugated one and two dimensional polymers

The band structures of some existing and hypothetical one and two dimensional conjugated polymers are examined in this work. The aim is to explore how the band gap sizes and the occurrence of partially filled bands are related to unit cell constitution and the geometrical disposition of the atoms in the unit cell. Among the polymers explored are poly-acetylene, polydiacetylene, polyphenylene, polyacene, graphite, boron nitride, polynitrile, polycyanonitrile, polypyridinopyridine, paracyanogen, the C3N net, (SN)x, (XCNSN)x, and C2S3N6 net.

The total synthesis of chlorophyll

Chlorophyll a, the major green pigment of the plant world, is certainly the most widespread and conspicuous of organic natural products. Few can be unaware of its decorative function, and all are beneficiaries of its central role in transforming sunlight into substance and sustenance. Yet the fruitful chemical study of this green badge of life did not commence until fairly recent times. For chlorophyll a is a very reactive, sensitive, and complicated substance. Only when, early in this century, the genius of Willstatter applied itself to the problem, were the first sure steps taken. That great investigator isolated the pigment-and its closely related frequent minor concomitant chlorophyll b as well-in the pure state, established correctly the empirical formula of the substance, and laid down a sound and extensive preliminary basis of transformation and degradation. These achievements can be measured against the fact that the isolation of chlorophyll in a state of purity is even now, after more than fifty years, no mean feat, and, further, that the empirical formula defined byWillstatter, repeatedly called into question by subsequent investigators, has stood the test of time. For some period after this solid foundation had been laid by Willstatter there was little activity until three new groups took the field late in the 1920s. Stoll, who had played a prominent role in the early studies as a collaborator of Willstatter, took up the work anew, and made important contributions, as did Conant in the United States. But by far the greatest contribution was made by Hans Fischer and his collaborators at Munich. Fresh from his dramatic conquest of the blood pigment, Fischer hurled his legions into the attack on chlorophyll, and during a period of approximately fifteen years, built a monumental corpus of fact. As this chemical record, almost unique in its scope and depth, was constructed, the molecule was transformed and rent asunder in innumerable directions, and the fascination and intricacy of the chemistry of chlorophyll and its congeners was fully revealed. These massive contributions were crowned by the proposal, in 1940, of a structure which was complete except for stereochemical detail. Finally, in a series of elegant investigations completed only during the last few years, Linstead and his associates at Imperial College were able to solve the stereochemical problem and to provide definitive confirmatory detail in respect of the number and disposition of saturated carbon atoms within the nuclear framework. Half a century of structural study had culminated in the complete formula (I) for chlorophyll aI, 8. Our active interest in chlorophyll was initiated four years ago, in 1956. The first questions we asked were very general ones. The structural investigations had been carried out almost entirely during the twilight of the classical period of organic chemistry. Only the very simplest basic * A brief communication recording the results on which this lecture is based has appeared in J. Am. Chern. Soc., 82, 3800 (1960).

The N-ethylbenzisoxazolium cation—I : Preparation and reactions with nucleophilic species

Abstract The preparation and properties of the N-ethylbenzisoxazolium cation are described. The cation is shown to react rapidly in aqueous solution with a wide variety of nucleophiles, yielding o-hydroxy-N-ethylbenzimido derivatives. With carboxylate, cyanate, or thiocyanate anions, or with thiourea, internal rearrangements occur, converting the imido adducts to O-substituted products. The reactions of N-alkylated benzisoxazoles generate a broad spectrum of unusual substances which are obtainable with difficulty by other routes and which may serve as starting materials for the synthesis of many hitherto-inaccessible systems.

The synthesis of L-()-mycarose and L-()-cladinose

Abstract Synthesis of cladinose from mycarose and synthesis of the same methylated derivative, 3,4-di-O-methylmycarose, from both mycarose and cladinose demonstrated the configurational identity of the two sugars. The synthesis of dl-mycarose and its 3-epimer by methods which reveal their configurations is described. Synthetic racemic mycarose was resolved via its bornanol-10-sulfonates and the active synthetic sugar has been shown to be identical with mycarose from natural sources. The isolation of L-lactic acid from carbon atoms 4, 5 and 6 mycarose proved that mycarose and cladinose belong to the L series of sugars. Mycarose has thus been shown to be 2,6-didesoxy-3-C-methyl-L-ribohexose, and cladinose its 3-methyl ether.

The reaction of isoxazolium salts with nucleophiles

Abstract A number of facile reactions of 3-unsubstituted isoxazolium salts with bases have been studied and are shown to proceed via the primary intermediacy of α-ketoketenimines. These experiments have resulted in the development of a general method for the synthesis of a variety of different heterocyclic systems. The reaction of isoxazolium salts with simple carboxylates has been examined in some detail, in view of the fact that the product enol esters are excellent acylating agents.

A useful synthesis of peptides

Abstract Carboxylates react rapidly and smoothly with 3-unsubstituted isoxazolium salts under very mild conditions to yield enol esters. In this paper we report the application of this reaction as the carboxyl-activating step in a simple and practical synthesis of peptides. The utility of the specific peptide forming reagent, N-ethyl-5-phenylisoxazolium-3′-sulfonate, is described in some detail.

The constitutions of cevine and some related alkaloids.

Die sauerstoffreichen Veratrum-Alkaloide gewinnen in letzter Zeit als blutdrucksenkende Arzneimittel immer mehr an Bedeutung. Darüber hinaus erwecken sie ein grosses Interesse vom Standpunkt des organischen Chemikers, da sie zu den kompliziertest gebauten niedrig molekularen Naturstoffen gehören. Bei der Konstitutionsaufklärung des Alkamins Cevin (XXXII), das eine Schlüsselstellung in dieser Reihe einnimmt, wurden unter anderem die folgenden neuen Ergebnisse erhalten: a) Die Konstitution zweier Abbauprodukte des Cevins — der Decevinsäure (XIII) und der « Hexan-tetracarbonsäure » (XVIII) — konnte bestimmt werden. b) Das sogenannte Anhydrocevin wurde als ein Orthoazetat XLII erkannt. c) Das Cevadin [XLI,R=CH3CH=C(CH3)CO], aus dem das Cevin durch alkalische Hydrolyse entsteht, gab bei milder Oxydation mit Chromsäure durch spontane Zyklisation des entstandenen Zwischenproduktes XLVII ein 7-Oxy-hydrindanon-(1)-Derivat (XLVI). Die Konstitution zweier Abbauprodukte des Cevins — der Decevinsäure (XIII) und der « Hexan-tetracarbonsäure » (XVIII) — konnte bestimmt werden. Das sogenannte Anhydrocevin wurde als ein Orthoazetat XLII erkannt. Das Cevadin [XLI,R=CH3CH=C(CH3)CO], aus dem das Cevin durch alkalische Hydrolyse entsteht, gab bei milder Oxydation mit Chromsäure durch spontane Zyklisation des entstandenen Zwischenproduktes XLVII ein 7-Oxy-hydrindanon-(1)-Derivat (XLVI).

Reaction of dimethyl sodio-3-ketoglutarate with glyoxal and substituted glyoxals: First expeditious preparation of bicyclo[3.3.0]octane-3,7-dione; synthesis and crystal structure of 5,7-dihydroxy-4-methoxycarbonyl-3-phenyl-1-indanone

Abstract A simple and efficient two-step preparation of bicyclo[3.3.0]octane-3,7-dione starting from the sodium enolate of dimethyl 3-ketoglutarate and glyoxal is described. This is an unprecedented case in which a condensation reaction of glyoxal is more successful under vigorous conditions (refluxing methanol) than under much milder ones (buffered water at ambient temperature). The major product (after hydrolysis-decarboxylation) from the analogous sequence with phenylglyoxal is 5,7-dihydroxy-4-methoxycarbonyl-3-phenyl-1-indanone, the result of a Dieckmann reaction in addition to the Michael and aldol reactions. Only the latter two occur in aqueous buffers, where the product after hydrolysis-decarboxylation is 1-phenylbicyclo[3.3.0]octane-3,7-dione. The X-ray crystal structure of the indanone reveals a novel hydrogen bonding phenomenon.

Intramolecular ene reaction of glyoxylate esters: an anisatin model study

Abstract A highly regio- and stereoselective Lewis acid catalyzed intramolecular ene reaction of the glyoxylate ester 9 has been used to synthesize the trihydroxylactone 2 .

Imidazole alkaloids of Macrorungia longistrobus: Revised structures and total syntheses

Abstract By total synthesis, it was shown that the imidazole alkaloids dehydroisolongistrobine and isolongistrobine possess structures 1 and 2 , respectively, rather than the structures proposed by Arndt, Eggers and Jordaan in 1969. Reaction of methyl 1-methylimidazole-5-carboxylate with phenylsulfonylmethyl magnesium bromide provided a β-ketosulfone which was alkylated with o -nitrobenzyl bromide to provide 6 . In the key step, amino alcohol 10 and tetrahydroquinoline 8 were obtained through aluminum amalgam reduction of 6. 8 was converted to isomacrorine 12. 10 could be converted to 1 by a three-step sequence; 2 was obtained from 10 by acylation with 4-pentenoyl chloride, oxidation, and osmium tetroxide catalyzed periodate cleavage of the vinyl group. Comparison of samples of synthetic alkaloids 1 and 2 with the corresponding alkaloids from natural sources showed that the natural and synthetic samples of each were identical.