Starting material definition

Both cis- and (rans-structures are possible RuH2(PMe3)4 is cis (Ru-H 1.507, 1.659 A, Ru-P 2.276-2.306 A) [90] while spectra show that RuH2(PF3)4 and others have this configuration. RuH2[PPh(OEt)2]4 is definitely trans (X-ray) with Ru-H 1.6 A, Ru-P 2.272 A. Many diphosphines form dihydrides. Ru(dmpe)2H2 has been a useful starting material for the synthesis of thiolate complexes [91] such as fra s-Ru(SPh)2(dmpe)2. 

All organic chemicals are, by definition, based on chemicals derived from living matter. Thus, the ten highest-volume commercial organic chemicals are all made from starting materials obtained from petroleum (oil) and natural gas, which are believed to have been formed by the microbial decomposition of ancient marine plants and animals. 

The alkyl ketone candidates With definition of the finasteride manufacturing process came a new challenge. The most efficient synthesis of the second generation candidate would make use of the penultimate in the finasteride process 33 as starting material (Scheme 3.25). With a pilot plant campaign to make 3 scheduled, realizing this objective became a priority. None of the methods reported in the literature for ester to ketone conversion had been applied to a hindered steroidal C17 ester. 

Fischer-Tropsch synthesis could be "tailored by the use of iron, cobalt and ruthenium carbonyl complexes deposited on faujasite Y-type zeolite as starting materials for the preparation of catalysts. Short chain hydrocarbons, i.e. in the C-j-Cq range are obtained. It appears that the formation and the stabilization of small metallic aggregates into the zeolite supercage are the prerequisite to induce a chain length limitation in the hydrocondensation of carbon monoxide. However, the control of this selectivity through either a definite particle size of the metal or a shape selectivity of the zeolite is still a matter of speculation. Further work is needed to solve this dilemna. 

The term carbometallation was most probably coined only about a quarter of a century ago.1 However, the history of those reactions that can be classified as carbometallation reactions is much older. If one includes not only the Ziegler-Natta-type organometallic alkene polymerization reactions2 but also various types of organometallic conjugate addition reactions,3 carbometallation collectively is easily more than a century old. In its broadest definition, carbometallation may be defined as a process of addition of a carbon-metal bond to a carbon-carbon multiple bond. As such, it may represent either a starting material-product relationship irrespective of mechanistic details or an actual mechanistic microstep of carbon-metal bond addition to a carbon-carbon metal multiple bond irrespective of the structure of the product eventually formed. 

The usual experimental approach3 is based on the Hammond postulate (Hammond, 1955). A transition state, which lies by definition between the starting materials and products for a particular step of a reaction, is supposed to be closer in structure, because closer in energy, to the higher energy species of the two. Various techniques, particularly linear free energy relationships, are available to compare the effects of various probes... 

In order to gain more insight into the intervention of the palladacycle, the following two substrates were subjected to the carbonylation with an icreased pressure of CO (15 atm). As a result, the starting materials were recovered intact without giving the cyclized products, which led to the definite conclusion that the 2-vinyl-2,3-dienyl ester is undoubtedly a precursor of the palladacycle (Scheme 16.37). 

Following our initial definition of the term cyclization reaction , the starting materials possess one donor site which is easily oxidized by one of the above-... 

It is the purpose of this section to provide the modern vocabulary required for the description of stereoselective reactions. This also implies the description of stereochemical aspects of starting materials and products, i.e., aspects of static stereochemistry. The material has been arranged in logical progression and, whenever possible, rules and directions for use or explicit definitions of important terms are given. 

The third approach is the main topic of this volume. According to the definition given above it involves enantiomerically pure starting materials which at some point must be provided by resolution or ex-chiral-pool synthesis. It is more or less equivalent to the term asymmetric synthesis defined by Marckwald in 19047 as follows Asymmetric syntheses are those reactions which produce optically active substances from symmetrically constituted compounds with the intermediate use of optically active materials but with the exclusion of all analytical processes . In today s language, this would mean that asymmetric syntheses are those reactions, or sequences of reactions, which produce chiral nonracemic substances from achiral compounds with the intermediate use of chiral nonracemic materials, but excluding a separation operation. 

There is no rigid definition of what constitutes a suitable synthesis. The major criterion by which syntheses are judged is the potential value to the scientific community. For example, starting materials or intermediates that are useful for synthetic chemistry are appropriate. The synthesis also should represent the best available procedure, and new or improved syntheses are particularly appropriate. Syntheses of compounds that are available commercially at reasonable prices are not acceptable. We do not encourage the submission of compounds that are unreasonably hazardous, and in this connection, less dangerous anions generally should be employed in place of perchlorate. 

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