Woodward method

For another possible mechanism that accounts for the stereochemical result of the Woodward method, sec Woodward Brutcher 7. Am. Chem. Soc. 1958, 80, 209. 

In order to study possible side reactions which may reduce the yield in the Woodward method of annulation of azetidin-2-ones (Scheme 31) similar reactions of ylides (214), which do not contain groups capable of conversion to carbonyl by DMSO-acetic anhydride treatment, have been investigated. 30 A range of products, e.g. (215) and (216), were obtained. A mild, four-carbon homologation of the 4-formyl-substituted azetidinone (217) involving reaction with the phosphonium ylide (218) has been used to synthesize (219), a useful intermediate in the synthesis of carbacephem antibiotics. 3 ... 

Heating stilbene with benzoyl peroxide and iodine in carbon tetrachloride at 80 °C for 48 h gives an 83% yield of the dibenzoyl ester of hydrobenzoin (l,2-dibenzoxy-l,2-diphenylethane) [230]. Esters of vicinal diols are intermediates in the preparation of diols by the Prevost and the Woodward methods (equation 78). 

Woodward method The syn-hydroxylation of an alkene the first step involves treating the alkene with iodine and silver acetate in a 1 1 molar ratio in wet acetic acid. The hydrolysis of the intermediate c/////-P-halogenoester is via a normal SN2 reaction in which there is no neighbouring group effect because the ester function is solvated by the water. Overall //-addition may be achieved by the method of Prevost. 

The Woodward-Hoffmann method [52], which assumes conservation of orbital symmetry, is another variant of the same idea. In it, the emphasis is put on the symmetries of molecular orbitals. Longuet-Higgins and Abramson [53] noted the necessity of state-to-state correlation, rather than the orbital correlation, which is not rigorously justified (see also, [30,44]). However, the orbital symmetry conservation rules appear to be very useful for most themial reactions. 

Frontier orbital analysis is a powerful theory that aids our understanding of a great number of organic reactions Its early development is attributed to Professor Kenichi Fukui of Kyoto University Japan The application of frontier orbital methods to Diels-Alder reactions represents one part of what organic chemists refer to as the Woodward-Hoffmann rules a beautifully simple analysis of organic reactions by Professor R B Woodward of Harvard University and Professor Roald Hoffmann of Cornell University Professors Fukui and Hoffmann were corecipients of the 1981 Nobel Prize m chemistry for their work... 

Woodward-Eschenmoser method, 4, 431-440 neo-Vitamin B,2, 4, 421 Vitamin C — see Ascorbic acid Vitamin E — see a-Tocopherol Vitamin K epoxide, 7, 119 synthesis, 1, 439 Vitamins heterocyclic... 

Equations 4-8 illustrate some mild methods that can be used to cleave amides. Equations 4 and 5 indicate the conditions that were used by Woodward and Eschenmoser, respectively, in their synthesis of vitamin B,2- Butyl nitrite," nitrosyl chloride, and nitrosoniurn tetrafluoroborate... 

P.R. Woodward, PPM Piecewise-Parabolic Methods for Astrophysical Fluid Dynamics, in Astrophysical Radiation Hydrodynamics (edited by K.A. Winkler and M.L. Norman), D. Reidel, Dordrecht, 1982. 

In the post-World War II years, synthesis attained a different level of sophistication partly as a result of the confluence of five stimuli (1) the formulation of detailed electronic mechanisms for the fundamental organic reactions, (2) the introduction of conformational analysis of organic structures and transition states based on stereochemical principles, (3) the development of spectroscopic and other physical methods for structural analysis, (4) the use of chromatographic methods of analysis and separation, and (5) the discovery and application of new selective chemical reagents. As a result, the period 1945 to 1960 encompassed the synthesis of such complex molecules as vitamin A (O. Isler, 1949), cortisone (R. Woodward, R. Robinson, 1951), strychnine (R. Woodward, 1954), cedrol (G. Stork, 1955), morphine (M. Gates, 1956), reserpine (R. Woodward, 1956), penicillin V (J. Sheehan, 1957), colchicine (A. Eschenmoser, 1959), and chlorophyll (R. Woodward, 1960) (page 5). ... 

Equations 1-10 illustrate some mild methods that can be used to cleave amides. Equations 1 and 2 indicate the conditions that were used by Woodward and Eschenmoser, respectively, in their synthesis of vitamin B12. Butyl nitrite, nitrosyl chloride, and nitrosonium tetrafluoroborate (NO BF4 ) have also been used to cleave amides. Since only tertiary amides are cleaved by potassium -butoxide (eq. 3), this method can be used to effect selective cleavage of tertiary amides in the presence of primary or secondary amides.(Esters, however, are cleaved by similar conditions.) Photolytic cleavage of nitro amides (eq. 4) is discussed in a review. 

Only in 1961 did Woodward and Olofson succeed in elucidating the true mechanism of this interesting reaction by making an extensive use of spectroscopic methods. The difficulty was that the reaction proceeds in many stages. The isomeric compounds formed thereby are extremely labile, readily interconvertible, and can be identified only spectroscopically. The authors found that the attack by the anion eliminates the proton at C-3 (147) subsequent cleavage of the N—0 bond yields a -oxoketene imine (148) whose formation was established for the first time. The oxoketene imine spontaneously adds acetic acid and is converted via two intermediates (149, 150) to an enol acetate (151) whose structure was determined by UV spectra. Finally the enol acetate readily yields the W-acyl derivative (152). 

In the perfect lattice the dominant feature of the electron distribution is the formation of the covalent, directional bond between Ti atoms produced by the electrons associated with d-orbitals. The concentration of charge between adjacent A1 atoms corresponds to p and py electrons, but these electrons are spatially more dispersed than the d-electrons between titanium atoms. Significantly, there is no indication of a localized charge build-up between adjacent Ti and A1 atoms (Fu and Yoo 1990 Woodward, et al. 1991 Song, et al. 1994). The charge densities in (110) planes are shown in Fig. 7a and b for the structures relaxed using the Finnis-Sinclair type potentials and the full-potential LMTO method, respectively. 

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