Organometallics in Synthesis

Novel catalyst systems have Included CoBrCPPha) 3-Bp3,OEt2 which selectively hydrogenates conjugated dienes to monoenes via 1,2-addition at the more substituted double bond (e.f. Equation 3) and KHCr2(CO)io which selectively reduces a,j8-unsaturated ketone or cyanides to the corresponding saturated ketone or cyanide.  

Two papers this year have described the use of chromate ions for the conversion of alkyl halides or alcohols into aldehydes or ketones (Equation 4). The reaction can be conducted in HMPA in the presence of a crown ether, and although yields are good for allylic and benzylic halides (ca. 80%) they are not so high for saturated halides. The chromate ion, however, can be supported on an insoluble polymer matrix as the tetra-alkylammonium salt and this both enhances the nucleophilicity of the ion and simplifies the work up procedure. Using the polymer-supported reagent a variety of primary and secondary alcohols were oxidized to the corresponding aldehyde or ketone in excellent yield (ca. 90%).  

Another useful synthesis of aldehydes and ketones involves the ruthenium catalysed amine A-oxide oxidation of alcohols. The reaction proceeds readily at room temperature and although a variety of A-oxides can be used the best yields 

Under acidic conditions VCI2 converts primary and secondary nitro-compounds into the corresponding carbonyl compound, e.g. (9) from (8). Yields with secondary nitro-compounds are moderate but with primary compounds the yields are much lower because the aldehydes produced react further under the strongly acidic reaction conditions. 

A simple dehydrogenation of the substituted cyclopentanone (10) with PdClj-chloranil produces the cyclopentenone (11) in ca. 70% yield. This one step conversion is particularly useful for small scale preparations. 

This report follows the format of previous years and once again, due 

The first example of a homogeneous metal-catalysed desulphurization 

Aryl alkyl ketones and aromatic aldehydes react with hydrogen under mild conditions in the presence of catalytic quantities of the 

The original report on the titanium-catalysed asymmetric epoxidation of allylic alcohols (Sharpless system) prescribed stoichiometric amounts of the titanium tartrate catalyst in the general procedure and many applications of this asymmetric epoxidation have been carried out using stoichiometric or near-stoichiometric amounts of the catalyst. Sharpless has reported the first general procedure for the asymmetric epoxidation of allylic alcohols using catalytic ( 10 %) amounts of titanium(IV) isopropoxide and diethyl tartrate. 

The key modification to the procedure is the presence of or 4A molecular sieves during the reaction. 

This Report follows the format established in previous years. We are conscious of the enormous increase in literature in transition-metal chemistry, and owing to limitations of space, the Report is more selective. This is especially true in the development of organopalladium chemistry in synthesis, where both new reactions and significant modifications to existing chemistry are being discovered at what seems to be an exponential rate. 

A timely review on the use of homogeneous asymmetric catalysts in the synthesis of chiral organic molecules has appeared. The review provides an excellent starting point for anyone considering adopting these methods in their synthetic strategy. 

One of the problems of asymmetric hydrogenation in synthesis is the apparent lack of predictability of the reactions. In an effort to develop a rational approach, Bosnich and his co-workers have investigated the effects of several chiral ligands for Rh catalysts during the asymmetric reduction of amino-acid precursors. This work provides some general conclusions that may prove useful in predicting optical yields from an asymmetric synthesis.  

Methods for achieving enantioselective reduction of prochiral ketones are always of interest. This can be achieved by asymmetric hydrogenation of corresponding enol diphenylphosphinates using a cationic rhodium complex of (/ )- -[(5)-r,2-bis(diphenylphosphino)-ferrocenyl]ethanol. Although optical yields of up to 78% are reported, only simple ketonic substrates were used further developments, therefore, would be welcome. 

Although aldimines can be reduced to amines by various reagents, the use of the Wilkinson catalyst in the presence of propan-2-ol as a hydrogen donor is an especially clean, mild, and easily operated method, which could well be translated into an asymmetric procedure. 

The format of this Report is similar to previous years. Several 

Alkylazides are reduced at 20 °C to the corresponding amines in good yields by KHFe(C0) under an atmosphere of carbon monoxide 

Reduction of the alcohol function of acetylenic alcohols without affecting the triple bond may be achieved by treating their [Co (C0)t] complexes with trifluoroacetic acid and sodium boro- 

Benzoyl cyanide generated in this way smoothly benzoylates amines in the presence of alcohols (91-99%). 

Secondary amines are oxidized to imines under similar mild con- 

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Main group organometallics in synthesis and transformations of heterocycles 98JCS(P1)1343. 

M. Schlosser, ed., Organometallic in Synthesis A Manual, Wiley, New York, 1994. 

Schlosser, M. Organoalkali Chemistry. In Organometallics in Synthesis - A Manual, Schlosser, M., Ed. Wiley Ghicester, 2002 Chapter 1. 

Wills, M. Main group organometallics in synthesis. Contemp. Org. Synth. 1996, 3, 201-228. 

M. Schlosser, Organometallics in Synthesis, 2nd Edn., John Wiley Sons, Chichester, 2002. 

Nozaki, in Organometallics in Synthesis A Manual, M. Schlossee (Fd.), Wiley Fngland, 1994, Chapt. 8, p. 535 and references cited therein. 

R. J. K. Taylor (Ed.), Organocopper Reagents, Oxford University Press, Oxford, 1994 m) B. H. Lipshutz in Organometallics in Synthesis, ScHLOSSER, M. (ed.), Wiley,... 

F. Totter and P. Rittmeyer, Organolithium Compounds—Industrial Applications and Handling , in Organometallics in Synthesis, A Manual (Ed. M. Schlosser), Wiley, New York, 2002. 

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