Selective hydroformylation

Selective hydroformylation of DCPD has afforded monoformyl derivatives (13), useful as perfume constituents and synthetic mbber intermediates (69) and dimethanohc derivatives useful for the manufacture of polycarbonates and polyesters (70). 

Bhattachaijee et al. [98] reported that nitrile rubber can be selectively hydroformylated in the presence of RhH(CO)(PPh3)3 and RhCl(CO)(PPh3)2 under high pressure of carbon monoxide and hydrogen. They found that RhH(CO)(PPh3)3 was more efficient than RhCl(CO)(PPh3)2. However, both catalysts offered se-... 

We describe here (i) the selective hydroformylation of 1,3-dienes to p,y-unsaturated aldehydes promoted by catalyst A and (ii) the efficient hydrosilylation of aromatic nitriles to A,iV-disilylamines using catalysts B and C. 

Selective Hydroformylation Catalysts Through Self-Assembly. 157... 

Scheme 2 Position-selective hydroformylation of internal alkenes with a rhodium(I)/-phosphabarrelene catalyst...

Most recently new applications for substrate-controlled branched-selective hydroformylation of alkenes substituted with inductively electron-with drawing substituents have emerged. A recent example is the hydroformylation of acrylamide with a standard rhodium/triphenylphosphine catalyst, which yields the branched aldehyde exclusively (Scheme 4) [40]. Reduction of the aldehyde function furnishes 3-hydroxy-2-methylpropionamide, which is an intermediate en route to methyl methacrylate. 

Table 1 Results of branched-selective hydroformylation of a.fi-unsaturated esters with a rhodium/phosphaadamantane (1) catalyst...

From a library of mixtures of monodentate ligands an excellent catalyst for branched-selective hydroformylation of methacrylic esters was identified (Scheme 5) [45]. The best catalyst employs a 1 1 mixture of triphenylphos-phine and a phosphabenzene ligand 2 [32]. 

Recently, a new bidentate hemispherical chelating bisphosphite ligand based on a calixarene backbone has been designed for linear selective hydroformylation of alkenes (Scheme 9) [54], Excellent levels of regioselectivity have been observed, and even the intrinsic branched-selective hydroformylation of styrene could be overruled by this system. However, the system suffers from low catalytic activity. 

A new chiral auxiliary based on a camphor-derived 8-lactol has been developed for the stereoselective alkylation of glycine enolate in order to give enantiomerically pure a-amino acid derivatives. As a key step for the synthesis of this useful auxiliary has served the rc-selective hydroformylation of a homoallylic alcohol employing the rhodium(I)/XANTPHOS catalyst (Scheme 11) [56]. 

Abu-Reziq, R., Alper, H., Wang, D.S. and Post, M.L. (2006) Metal supported on dendronized magnetic nanopartides highly selective hydroformylation catalysts. Journal of the American Chemical Society, 128 (15), 5279-5282. 

One of the most selective hydroformylation catalysts was obtained when cobalt acetate was irradiated in the presence of an excess of a phosphine, with synthesis gas at 80 atm, in methanol as the solvent. Propylene was hydroformylated with this catalyst to give butyraldehyde with an n/i ratio of more than 99/1 /10/. In the absence of phosphine, the cobalt acetate forms a more active catalyst which is, however, less selective for straight chain products /23/. 

It is interesting to note that using the sol-gel procedure (I) the pre-formation of the rhodium diphosphine complex suppressed the formation of ligand free rhodium-cations on the silica surface. This approach gave rise to a well-defined, very selective hydroformylation catalyst. All immobilised catalysts were 10 to 40 times slower than the homogeneous catalyst under the same conditions, the sol-gel procedure yielding the fastest catalyst of this series. 

More recently, during research aimed at supporting the highly linear selective hydroformylation catalyst [Rh(H)(Xantphos)(CO)2] onto a silica support, the presence of a cationic rhodium precursor in equilibrium with the desired rhodium hydride hydroformylation catalyst was observed. The presence of this complex gave the resulting catalyst considerable hydrogenation activity such that high yields of linear nonanol could be obtained from oct-1-ene by domino hy-droformylation-reduction reaction [75]. 

Although early catalysts were based on cobalt, nowadays, rhodium catalysts are preferred because they require lower pressure and afford higher chemo- and regioselectivity [1,2]. In recent years, extensive research into the production of only linear aldehydes has provided impressive results. The application of phosphines with a wide bite angle in the rhodium catalyzed hydroformylation of terminal alkenes enable the regioselectivity to be almost totally controlled [3]. Branched selective hydroformylation, al-... 

Tab. 6.3 Selected hydroformylation experiments with polymeric amphiphiles (experimental data are listed in Scheme 5.5, reaction time = 3 h).

Figure 2 Union Carbide bis-phosphite ligands for normaZ-selective hydroformylation.

Figure 16 BISBI 4 and its sulfonated derivatives 44a-c for normaZ-selective hydroformylation in aqueous/organic biphasic media.

The combination of rhodium dicarbonyl acetylacetonate complex (Rh(acac)(CO)2) and a diphosphite ligand, (2,2 -bis[(biphenyl-2,2 -dioxy)phosphinoxy]-3,3 -di-/i t/-butyl-5,5 -dimethoxy-l,T-biphenyl (BIPHEPHOS), is an excellent catalyst system for the linear-selective hydroformylation of a wide range of alkenes. This catalyst system has been successfully applied to the cyclohydrocarbonylation reactions of alkenamides and alkenylamines, which are employed as key steps for the syntheses of piperidine,indolizidine, and pyrrolizidine alkaloids. ... 

A quinazoline alkaloid skeleton has been synthesized by means of the Rh-catalyzed cyclohydrocarbonylation of diaminoalkenes. The reaction of 2-(A -allylaminomethyl)aniline 55 gave quinazoline 59 in excellent yield through the highly linear-selective hydroformylation of 55 to aldehyde 56, followed by the sequential formations of hemiaminal 57 and iminium ion 58 as intermediates and then the subsequent intramolecular amine addition (Scheme In the same manner, the reaction of A -allyl-2-aminomethylaniline 60 afforded 61 in 96% yield. ... 

This practical and highly selective hydroformylation protocol, which omits the need for special pressure equipment, should find wide application in organic synthesis. 

Complexes of carbonic or carboxylic acid anions have been used as hydroformylation catalysts for various alkenes. The bicarbonate complex [Rh(H)2(02COH)(PPr 3)2] as catalyst enabled 1-hexene to be converted to aldehydes using paraformaldehyde as source of hydrogen and carbon monoxide in place of the more usual gas mixture.338 The acetate complex [Rh(OAc)CO(PPh3)2] (74) has been shown to effect the selective hydroformylation of cyclic dienes. The cyclohexadienes gave predominantly dialdehydes, whereas 1,3- and 1,5-cyclooctadiene gave the saturated monoaldehydes.339... 

Although /V-methyltetrahydropyridines are not selectively hydroformylated, an equal mixture of the two aldehydes being obtained from /V-methy 1-1,2,3,6-tetrahydropyridine, W-methyltropidenes are selectively formylated at the 3-position (equation 29). The difference in the selectivity can be attributed to the substitution in tropidine (bridge head carbon). 

Platinum complexes, [PtCl2 (l ,l )-XantBino ] (2) and its S,S analogue, were treated with tin(II) chloride to form the pre-catalyst for chemo-, regio-, and enantio-selective hydroformylation of styrene, vinyl acetate and allyl acetate. Although the reaction showed good chemo- and regio-selectivities, only moderate ee was obtained.103... 

A range of high-yielding quaternary selective hydroformylation reactions have been performed in the presence of a reactive phosphane-modified rhodium catalyst at... 

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