The exploitation of various homogeneous catalytic reactions in organic syntheses can be considered as a real 'break-through' of the chemistry of the past few decades. This review comprises some recent results on the transition metal catalysed homogeneous carbonylation reactions dealing with the synthesis of practically important compounds. Selected examples are given for both the functionalization of various biologically important skeletons and their build-up from appropriate building blocks via carbonylation reactions by using carbon monoxide as a 'carbonyl- source'. The short review illustrates, that hydroformylation, the industrially most important carbonylation reaction has also gained importance in the functionalization of steroidal compounds providing a formyl functionality for further 'build-up' of the skeleton. Enantioselective hydroformylation reaction provides an efficient way to synthesise intermediates of non-steroidal anti-inflammatory agents (NSAI), like Ibuprofen. Alcohols can also be used as hydrogen donors in carbonylation reactions of unsaturated substrates like olefins and acetylenes. Saturated and unsaturated esters can be obtained in hydroalkoxycarbonylation reaction, respectively. Using enol triflates or iodo-alkenes as substrates (possessing a trifliloxy or iodo leaving group) various conjugated unsaturated esters and amides can be synthesised in excellent yields in the presence of alcohol or amine nucleophiles. The strength of these palladium catalysed homogeneous alkoxycarbonylation and aminocarbonylation reactions has been shown by examples of pharmaceutical importance (tropinone and steroid derived compounds). The intramolecular alkoxycarbonylation and aminocarbonylation reactions became a widely used tool for the synthesis of lactones and lactames, respectively. A range of cyclic compounds of biological importance has been synthesised by using this methodology. The efficiency of the consecutive use of these two carbonylation reactions has been shown by the synthesis of steroidal compounds functionalized at the A- and D-rings. Similar compounds of potential 5α-reductase inhibitor properties have been synthesised in hydrazinocarbonylation reaction by using substituted hydrazines as nucleophiles. Hydroxamates can also be easily obtained by the use of hydroxylamine derivatives as nucleophiles by following a similar reaction protocol. Even cross-coupling reactions (e.g. Stille coupling) can be carried out under carbon monoxide atmosphere and unsaturated ketones or aryl ketones are available in this way. Pauson-Khand reaction plays a peculiar role among carbonylative ring closure reactions both from mechanistic and synthetic point of view. The [2+2+1] type cycloaddition reaction takes place via the activation of an acetylene by dicobalt-octacarbonyl, which reacts with an alkene providing a metallacyclopentene (cobaltacyclopentene). Upon insertion of carbon monoxide into the metal-carbon bond a metallacyclohexanone is formed that undergoes reductive elimination and provides cyclopentenone derivatives. The intramolecular version of Pauson-Khand reaction proved to be a basic synthetic method for the synthesis of natural polycyclic compounds. The homogeneous catalytic reactions (and carbonylation reactions among them) provide efficient ways for the synthesis of compounds of practical importance. Their applications can be extremely advantageous by shortening multistep synthetic routes and by providing high yields and selectivities. Some of the 'green chemistry requirements' can also be met by the application of various transition metal catalysed reactions.
|Number of pages||8|
|Journal||Magyar Kemiai Folyoirat, Kemiai Kozlemenyek|
|Publication status||Published - Mar 1 2004|
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