Early attempts

With the advent of quantum mechanics, quite early attempts were made to obtain methods to predict chemical reactivity quantitatively. This endeavor has now matured to a point where details of the geometric and energetic changes in the course of a reaction can be calculated to a high degree of accuracy, albeit still with quite some demand on computational resources. 

Asymmetric cyclization using chiral ligands has been studied. After early attempts[142-144], satisfactory optical yields have been obtained. The hexahy-dropyrrolo[2,3-6]indole 176 has been constructed by the intramolecular Heck reaction and hydroaryiation[145]. The asymmetric cyclization of the enamide 174 using (S j-BINAP affords predominantly (98 2) the ( )-enoxysilane stereoisomer of the oxindole product, hydrolysis of which provides the ( l-oxindole aldehyde 175 in 84% yield and 95% ec. and total synthesis of (-)-physostig-mine (176) has been achieved[146]. 

An early attempt to hydroformylate butenediol using a cobalt carbonyl catalyst gave tetrahydro-2-furanmethanol (95), presumably by aHybc rearrangement to 3-butene-l,2-diol before hydroformylation. Later, hydroformylation of butenediol diacetate with a rhodium complex as catalyst gave the acetate of 3-formyl-3-buten-l-ol (96). Hydrogenation in such a system gave 2-methyl-1,4-butanediol (97). 

Gums and starches were used in early attempts to replace the viscosity and lubricity of oils in foods. These were not well received by consumers because they assumed fats merely suppHed mouthfeel and a bit of flavor. On closer examination, it became evident that fats in food and in the diet performed many roles, some simple, some extremely complex, some understood, and some not understood. 

Several attempts have been made to determine proper scaling relationships for Group B fluidized beds. These early attempts, and a rigorous... 

Leather (qv) has been employed for many uses since ancient time on account of the convertibiUty of an easily decomposed substance into one which resists putrefaction. Leather is stUl an important material with its unique stmcture it is so dense in texture that it resists wind and water while retaining breathabihty and flexibiUty, which makes the resulting goods comfortable. Early attempts to imitate leather included appHcation of oil, mbber, or soluble cotton onto paper or fabrics. However, very Htde progress had been made until the era of synthetic resins began in the twentieth century. 

Interaction Parameters. Early attempts to describe PVC—plasticizer compatibiHty were based on the same principles as used to describe solvation, ie, like dissolves like (2). To obtain a quantitative measure of PVC—plasticizer compatibihty a number of different parameters have been used. More recently these methods have been assessed and extended by many workers (7—9). In all cases it is not possible to adequately predict the behavior of polymeric plasticizers. 

The potential usefulness of elfamycins as growth promoters and feed-conversion enhancers is now generally recognized. Low original fermentation yields and difficulties in yield improvements discouraged early attempts to develop aurodox ( 1, R = CH ) and mocimycin (kirromycin) (1, R = H) commercially. 

Total Synthesis. Poor yields encountered duriag the manufacture of vitamin D stimulated early attempts to synthesize vitamin D. In 1959 Inhoffen synthesized vitamin from 3-methyl-2-(2-carboxyethyl)-2-cyclohexenone (40), uskig the Wittig reaction extensively (103). 

Early attempts to produce cephalosporin analogs by varying the 7-acylamino substituent were frustrated because, in contrast to previous experience with penicillins, a good method for producing the necessary 7-amino compound (33a) could not be found. This problem was finally solved when it was discovered that diazotization of the a-aminoadipyl residue produces an iminolactone (33b) which can be hydrolyzed to the free amine in good yield. Subsequently an improved procedure was developed which involves silylation of the carboxyl groups followed by reaction with phosphorus pentachloride to yield iminochloride (33c)... 

Early attempts to apply the Sheehan penicillin synthetic strategy to the total synthesis of cephalosporins were not particularly successful. Although the key step, formation of the /3-lactam CO—N bond, could be carried out efficiently (46->47), subsequent conversion of the lactone to a free C-4 carboxyl could only be accomplished in poor yield (B-72MI51007). 

Different side chains have been found to have weak but definite preferences either for or against being in a helices. Thus Ala (A), Glu (E), Leu (L), and Met (M) are good a-helix formers, while Pro (P), Gly (G), Tyr (Y), and Ser (S) are very poor. Such preferences were central to all early attempts to predict secondary structure from amino acid sequence, but they are not strong enough to give accurate predictions. 

Early attempts to metalate 1,1-difluoroethylene with -butyllithium in tetra-hydrofuran or diethyl ether were unsuccessful. Another example whereby the course of the reaction may be altered by substitution of rec-butyllithium in place of n-butyllithium is the metalation of 1,1 -difluoroethylene [60] (equation 26)... 

Early attempts at deducing functionals for the kinetic and exchange energies considered a non-interacting uniform electron gas. For such a system it may be shown that T[p] and K[p] are given as... 

Early attempts to prepare 5-amino- and 5-acylaminobenzofuroxans by hypochlorite oxidation of the corresponding o-nitroanilines met with failure. Pyrolysis of the appropriate azide, however, gives 5-dimetliylamino- and 5-acetamidobenzofuroxan, whereas urethans of type (33) are produced by Curtius degradation of the 5-carboxylic acid. Controlled hydrolysis of the acetamido compound and the... 

An early attempt to synthesize rutaecarpine (111) from the urea derivative 110 by a method analogous to that of Clemo and Swan was unsuccessful. ... 

Early attempts to study the structure of thiazol-2-one by comparison of its ultraviolet spectrum with those of both alkylated forms failed because of the similarity of the spectra in the region investigated. However, in 1935, this method was successfully applied to bcnzothiazol-2-one (93) and in 1954 to thiazol-2-one itself,indi-... 

It is common practice today to use the term "alloy" in connection with specific classes of materials, with prominence given to metals and semiconductors. However, there is good justification for considering alloys in a unified manner based on properties rather than types of materials because, after all, to alloy means to mix. The scientific aspects of mixing together different materials has a very long history going back to early attempts to understand and control materials behavior for the service of mankind. 

Jars provide an upward or downward shock (or Jar) to the entire drill string. Early attempts to recover stuck drill pipe motivated the development of Jars. 

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