Stoichiometric reagents, synthetic methods

In fact, although good enantioselectivities in ADH of dialkyl substituted olefins could be previously obtained through the use of stoichiometric reagents at low temperature [34], the catalytic ADH developed by Sharpless is by far the best method that the synthetic organic chemist has presently at his hands. l... 

Several synthetic methods are available for the preparation of Fc peptide conjugates, of which the active ester method is most compatible with biological environments.41 This method works under mild conditions with an isolable FcCO-active ester, in which reactive heterocyclic isolable esters are formed. These can be isolated or reacted in situ with suitable peptides to give the desired Fc-peptide conjugate. These active esters can be used as stoichiometric Fc delivery reagents, which make them suitable for automated solid-phase synthesis of Fc-peptide conjugates. 

Asymmetric allyation of carbonyl compounds to prepare optically active secondary homoallyhc alcohols is a useful synthetic method since the products are easily transformed into optically active 3-hydroxy carbonyl compounds and various other chiral compounds (Scheme 1). Numerous successful means of the reaction using a stoichiometric amount of chiral Lewis acids or chiral allylmetal reagents have been developed and applied to organic synthesis however, there are few methods available for a catalytic process. Several reviews of asymmetric allylation have been pubHshed [ 1,2,3,4,5] and the most recent [5] describes the work up to 1995. This chapter is focussed on enantioselective allylation of carbonyl compounds with allylmetals under the influence of a catalytic amount of chiral Lewis acids or chiral Lewis bases. Compounds 1 to 19 [6,7,8,9,10,11,12,... 

The replacement of stoichiometric reagents with a catalyst is an efficient method of increasing the atom economy of synthetic transformations and is an area that has benefited greatly from the coupling of solid-supported catalysts with flow reactor methodology, not only from a product purity perspective but also as a means of increasing catalyst lifetimes. 

Organoindium halides can readily be prepared by many of the synthetic methods outlined for the preparation of organoindium derivatives, but with stoichiometric control to afford the organoindium halide derivative. For example, (a) reaction of InXa with less than three equivalents of a lithium or Grignard reagent (equations 12-13), (b) reaction of Rsin with HX, which proceeds by elimination of a simple organic moiety (equation 14), (c) a redistribution reaction between InXa and Rain (equations 15-16). 

Transient carbenes display a rich and diverse chemistry as stoichiometric reagents, for example, in reactions such as olefin cyclopropanation, C-H insertion, dimerization, 1,2-migration, and so on. Carbenes are important in several synthetic methods and are growing in importance, especially the intramolecular versions. Carbenes are electron deficient, and unless strong resonance interaction is possible the reactions will be electrophilic. The chemical behavior of a carbene depends to some extent on its method of preparation, electronic state, and also on the presence or absence of certain metals or metallic salts. The state in which the carbene is produced depends on the method of generation, that is, singlets... 

One-electron reduction or oxidation of organic compounds provides a useful method for the generation of anion radicals or cation radicals, respectively. These methods are used as key processes in radical reactions. Redox properties of transition metals can be utilized for the efficient one-electron reduction or oxidation (Scheme 1). In particular, the redox function of early transition metals including titanium, vanadium, and manganese has been of synthetic potential from this point of view [1-8]. The synthetic limitation exists in the use of a stoichiometric or excess amount of metallic reductants or oxidants to complete the reaction. Generally, the construction of a catalytic redox cycle for one-electron reduction is difficult to achieve. A catalytic system should be constructed to avoid the use of such amounts of expensive and/or toxic metallic reagents. 

Metal carbonyl cluster compounds which contain three ruthenium or three osmium atoms in the cluster core are common.1 Potentially useful reagents for syntheses of these compounds are the triruthenium and triosmium dianions [M3(CO)h]2 (M = Ru, Os).2 Therefore, it is desirable to develop good synthetic routes to obtain [M3(CO)11]2- (M = Ru, Os) of high purity in high yields. A method that is particularly useful for generating [M3(CO)n]2 (M = Ru, Os) is the designed stoichiometric reduction of M3(CO)12 (M = Ru, Os) using an electron carrier such as potassium-benzophenone.3... 

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