With rhodium synthesis

There are several examples of intramolecular reactions of monocyclic /3-lactams with carbenes or carbenoids most of these involve formation of olivanic acid or clavulanic acid derivatives. Thus treatment of the diazo compound (106) with rhodium(II) acetate in benzene under reflux gives (107), an intermediate in the synthesis of thienamycin (80H(14)1305, 80TL2783). 

A novel chiral dissymmetric chelating Hgand, the non-stabiUzed phosphonium ylide of (R)-BINAP 44, allowed in presence of [Rh(cod)Cl]2 the synthesis of a new type of eight-membered metallacycle, the stable rhodium(I) complex 45, interesting for its potential catalytic properties (Scheme 19) [81]. In contrast to the reactions of stabihzed ylides with cyclooctadienyl palladium or platinum complexes (see Scheme 20), the cyclooctadiene is not attacked by the carbanionic center. Notice that the reactions of ester-stabilized phosphonium ylides of BINAP with rhodium(I) (and also with palladium(II)) complexes lead to the formation of the corresponding chelated compounds but this time with an equilibrium be-... 

In another study (102), a triarylphosphine with a sulfonyl group on each phenyl was prepared and used with rhodium in a buffered aqueous system. The hydroformylation of propylene was conducted at 80°C and 50 atm of synthesis gas. The yield of aldehydes was 98% on converted propylene with an n iso ratio of 6.7 1. 

Subsequent examination of a tethered alkyne-VCP with rhodium(i) resulted in the first metal-catalyzed [5 + 2]-reaction. Excellent yields were obtained with a variety of substrates (Scheme 3) irrespective of the steric and electronic nature of the R1 group. Notably, quaternary centers are accessed in high yield. Since this first report, in-depth studies on catalysts, substrate scope, selectivity, and applications to total synthesis have been carried out. Work in this area has been reviewed.23-26... 

Although aldehydes obtained through the hydroformylation of dihydrofurans are interesting building blocks for organic synthesis, few studies have been reported on the subject. In 1998, previous work on the control of the regio-selectivity in the hydroformylation of dihydrofurans has been reported with rhodium systems modified with different ligands [77,78]. In the hydroformylation of 2,5-dihydrofuran 46 the expected product is the tetrahydrofuran 3-carbaldehyde 49 (Scheme 7). 

The perfluoroacetamide catalysts, rhodium(II) trifluoroacetamidate [Rh2(tfm)4] and rhodium(II) perfluorobutyramidate [Rh2(pfbm)4], are interesting hybrid molecules that combine the features of the amidate and perfluorinated ligands. In early studies, these catalysts were shown to prefer insertion over cycloaddition [30]. They also demonstrated a preference for oxindole formation via aromatic C-H insertion [31], even over other potential reactions [86]. In still another example, rhodium(II) perfluorobutyramidate showed a preference for aromatic C-H insertion over pyridinium ylide formation, in the synthesis of an indole nucleus [32]. Despite this demonstrated propensity for aromatic insertion, the perfluorobutyramidate was shown to be an efficient catalyst for the generation of isomtinchnones [33]. The chemoselectivity of this catalyst was further demonstrated in the cycloaddition with ethyl vinyl ethers [87] and its application to diversity-oriented synthesis [88]. However, it was demonstrated that while diazo imides do form isomtinchnones under these conditions, the selectivity was completely reversed from that observed with rhodium(II) acetate [89, 90]. 

As Moody and co-workers (173) discovered, isomtinchnones can occasionally form even when they are not the desired product Thus, these workers inadvertently obtained an oxazolidinedione via an isomtinchnone rather than the desired oxoindo-line when a diazo compound was treated with rhodium(II) perfluorobutyramide in their studies leading ultimately to a synthesis of the marine alkaloid convolutamy-dine C. 

For examples with rhodium catalysts, see Fell Beutler Tetrahedron Lett. 1972, 3455 Botteghi Salomon Tetrahedron Lett. 1974,4285. For an indirect method, see Campi Fitzmaurice Jackson, Perlmutter Smallridge Synthesis... 

Under mild conditions, hydroformylation of olefins with rhodium carbonyl complexes selectively produces aldehydes. A one-step synthesis of oxo alcohols is possible using monomeric or polymeric amines, such as dimethylbenzylamine or anion exchange resin analog to hydrogenate the aldehyde. The rate of aldehyde hydrogenation passes through a maximum as amine basicity and concentration increase. IR data of the reaction reveal that anionic rhodium carbonyl clusters, normally absent, are formed on addition of amine. Aldehyde hydrogenation is attributed to enhanced hydridic character of a Rh-H intermediate via amine coordination to rhodium. 

Asymmetric hydroformylations of all the above types have been achieved with rhodium catalysts enantioface- and enantiomer-discriminating hydroformylations also occur with cobalt and platinum catalysts whereas with ruthenium or iridium complexes only enantioface-discriminating synthesis has been reported up to now (see Sect. 2.1.4.). 

Friedrich et al. [28] describes a method of recycling a rhodium catalyst via thermal separation. The rhodium, which is fixed on a layer, is dissolved into the solution, in which triphenylphosphine stabilizes the rhodium. The reaction is carried out in a reactor with a synthesis gas pressure of 60 bar and at 120°C. After the reaction, the carrier is filtered before the product, methyl formylstearate, is separated by distillation. The rhodium-containing residue is united with the carrier before the organic... 

Catalyst Description. The LPO catalyst is a triphenylphosphine modified carbonyl complex of rhodium. Triphenylphosphine, carbon monoxide, and hydrogen form labile bonds with rhodium. Exotic catalyst synthesis and complicated catalyst handling steps are avoided since the desired rhodium complex forms under reaction conditions. Early work showed that a variety of rhodium compounds might be charged initially to produce the catalyst. Final selection was made on the basis of high yield of the catalyst precursor from a commodity rhodium salt, low toxicity, and good stability to air, heat, light, and shock. 

Scheme 46 Synthesis of ligand precursor 66 and complexation with rhodium(I) 67...

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