Organometallic thiocarbonyls

Organometallic betaines of type I can be considered as the closest structural analogs of carbon betaines of the (+ )P-C-C-X( ) type (IV), which were regarded for a long time as possible intermediates in classical reactions of carbonyl and thiocarbonyl compounds with phosphorus ylides (Wittig and Corey-Chaykovsky reactions and related processes,5,6 Scheme 1). Vedejs and coworkers7,8 proved unambiguously that oxapho-sphetanes (III) are true intermediates in the reactions of nonstabilized phosphorus ylides with carbonyl compounds. The formation of oxabetaines (+)p-c-c-o(-> was detected only in the form of their adducts with lithium salts.9,10... 

Free radical addition to oximes and oxime ethers emerged as a useful alternative to addition of organometallic reagents, particularly for intramolecular reactions. The most important advantage of free radical V5. organometallic addition is its tolerance for almost any functional group (with the exception of thiocarbonyl and iodoalkyl functions). 

The preparations of several (arene)(thiocarbonyl)chromium(0) complexes bearing electron-donating and/or electron-withdrawing substituents on the ring are described here (A-E). This type of compound is useful in organometallic chemistry for problems related to stereochemistry around a chromium atom6 and in organic chemistry in the activation of arene substituents with respect to alkylation.7... 

In this chapter, the recent advances in amidocarbonylations, cyclohydrocarbonylations, aminocarbonylations, cascade carbonylative cyclizations, carbonylative ring-expansion reactions, thiocarbonylations, and related reactions are reviewed and the scope and mechanisms of these reactions are discussed. It is clear that these carbonylation reactions play important roles in synthetic organic chemistry as well as organometallic chemistry. Some of the reactions have already been used in industrial processes and many others have high potential to become commercial processes in the future. The use of microwave irradiation and substitutes of carbon monoxide has made carbonylation processes suitable for combinatorial chemistry and laboratory syntheses without using carbon monoxide gas. The use of non-conventional reaction media such as SCCO2 and ionic liquids makes product separation and catalyst recovery/reuse easier. Thus, these processes can be operated in an environmentally friendly manner. Judging from the innovative developments in various carbonylations in the last decade, it is easy to anticipate that newer and creative advances will be made in the next decade in carbonylation reactions and processes. 

Many examples of the nucleophilic attack of organometallic compounds at the sulfur atom of thiocarbonyl groups were reported in the 1970s by Beak, Vialle, Ohno, Schaumann and their co-workers [119, 120, 327-329]. This thiophilic addition opens the way for a new method of preparation of carbanions a to sulfur. 

Although due to limitations in space organometallic applications lie beyond the scope of this overview, their increasing use in recent years for the generation and stabilization of thiocarbonyls will be summarized briefly in this section and leading references will be given. 

In Section III.K we have briefly summarized the major advances in the preparation of thiocarbonyl compounds stabilized by organometallics. The synthetic applications of this kind of reagents have experienced impressive growth in recent years and major contributions will be collected in this section, although the interested reader is referred to specialized Serials on this subject. 

Organometallic thioketones behave as dienophiles in the reactions with cyclopenta-diene497 and also undergo attack by butyllithium to give mostly reaction at the thiocarbonyl sulfur. The organometallic moiety (ferrocenyl, Mn complex etc.) is inert under these reaction conditions498. 

Carbonyl and Thiocarbonyl Complexes.—For a comprehensive survey the reader should consult the Organometallic Specialist Periodical Report. 

So far we have considered sulfur-containing carbanions obtained by metallation with appropriate bases of a to sulfur atom(s) acidic C-H bonds. For synthetic purposes this method has been by far the most used. Among the variety of other routes to such carbanions [203] we shall consider two methods which seem to be general and promising the reductive lithiation of phenyl thioethers and the thiophilie addition of organometallics to thiocarbonyl compounds (vide infra Section 4.1.2). 

Reactions of thoiminium salts, generated in situ from thioamides and methyl triflate (MeOTf), with two different alkylmetals such as alkynyllithiums and alkylmagnesium bromides have been studied. The two different organometallic reagents have been nucleophilically introduced to the carbon atom of the thiocarbonyl group of thiamides to afford tertiary propargylamines in one-pot procedure (Scheme 36). ... 

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