Acetate catalyzed system

An example of the vinylogous reactivity is the reaction of 52 with cyclopentadiene (Tab. 14.9) [77]. Rhodium(II) acetate-catalyzed decomposition of 52 in dichloro-methane, yields a 2 1 mixture of the bicyclic system 53 derived from the [3-1-4] cycloaddition, and the bicyclo[2.2.1]heptene 54 resulting from electrophihc attack at the vinylic position followed by ring closure. When Rh2(TFA)4 is used as the catalyst, bicy-clo[2.2.1]heptene 54 becomes the dominant product, while the reactivity of the vinyl terminus is suppressed using a hydrocarbon solvent as observed in the Rh2(OOct)4-cat-alyzed reaction in pentane, which affords a 50 1 ratio of products favoring the [3-1-4] cycloadduct 53. 

Reaction 4 shows that the ruthenium center with three coordinated carbonyls can transfer one such ligand to the piperidine (presumably coordinated). The mechanism suggested for the acetate complex includes exactly analogous steps (Reactions 6 and 7). The kinetics for the hydride-catalyzed system, however, are quite different and show a first-order dependence in Ru and a more complex dependence on CO (Figure 4). Further, no autocatalysis is evident. 

A group at Industrial Research Limited in New Zealand recently reported the results of a study to determine if a cross-linked enzyme crystal-catalyzed resolution can compete with alternative chiral technologies in the pharmaceutical and chemical process industries. The group used the enantioselective hydrolysis of a-phenylethyl acetate catalyzed by ChiroCLEC -PC as a model system (Fig. 13). Based on their results with 270 kg of racemate, they evaluated the economics of mnning the process at the 600-kg batch scale and concluded that this process is economically feasible [38],... 

Additions to l,3-dienes6 (12, 367-368 14, 249-250 15, 245). This reaction can be used to effect intramolecular cyclization of cyclic 1,3-dienes substituted by a suitable nitrogen nucleophile. Thus reaction of the amido diene 1 with lithium acetate catalyzed by Pd(OAc)2 (with benzoquinone as reoxidant) provides the ds-fused heterocycle cis-2, in which the acetoxy group is cis to the ring fusion, formed by an overall trans-1,4-oxyamidation of the diene system. Addition of a trace of LiCl improves the yield and results in an overall cis- 1,4-oxyamidation (equation I). Acetamides and carbamates can also be used in place of amides. 1,4-Chloroamidation can also be effected by use of 2 equiv. of LiCl. 

Rhodium acetate-catalyzed diazo decomposition has been used in a synthesis of the pyrrole 51, illustrating a route to several similar 3-oxypyrrole systems (Equation 11) <2002SL1913>. Similar annulations of some related fluorine containing substrates resulted in various unusual fluoropyrrole derivatives <20030L745>. 

An intramolecular carbenoid addition onto a carbon-carbon double bond provides a possible synthetic route to the pyrrolidine ring. The rho-dium(II) acetate-catalyzed reaction of diazo amide 106 leads to a mixture of diastereomers 107 and 108 (6 1) in 43% yield (88TL1181). The decomposition of AjA-diallyl-a-diazoacetamide catalyzed by Rh2(55-MEPY)4 forms product 109 from an enantioselective intramolecular cyclopropanation (50% yield, 72% e.e.) (94T1665). Spiro-fused ring systems were produced by this route from quinonediazides 110 and 111 under irradiation (83TL4773 86TL2687). 

Cyclopropanation of Norbornene and Related Systems with (2-Siloxyallyl) Acetates Catalyzed by Pallad-ium(O) General Procedure ... 

Aldiough the Nicholas reaction is a reliable method for propargylation of silyl enolates, it requires a stoichiometric amount of alkyne-Co2(CO)6 complexes [260]. Recently, Matsuda et al. successfully used the Ir-catalyzed system for highly regioselective propargylation of silyl enolates with propargyl acetates (Scheme 10.97) [261]. 

Padwa and co-workers have reported" that the rhodium(II) acetate catalyzed ring opening of the cyclopropene 75 results in the formation of the bicyclic system 78 of undefined stereochemistry in 52% yield (Scheme 27). It is considered that the reaction occurs by ring opening of 75 to the vinylcarbenoid 76. Cyclization of 76 produces the fiiran 77, which on reaction with a second equivalent of 76 forms the [344] annulation product 78. 

Other stereogenic centers may be used to control the stereochemistry of the seven-membered ring. Rhodium(II) acetate catalyzed decomposition of 105 results in the formation of the tricyclic systems... 

In this example, prior to water addition, alcoholysis causes the sol to consist primarily of TEOS in 4 equivalents of acetic acid. Thus the question becomes, why does TEOS gel much faster in acetic acid than in ethanol Figure 48.5 shows Si NMR spectra for the Si(OAc)4-ethanol system just described and for TEOS in 4 mol of acetic acid, both spectra taken 45 min after addition of 4 mol of 1 M HCl. No evidence is seen in the NMR spectra for substitution of ethoxide ligands by acetate in the TEOS-acetic acid system. The two spectra are similar. (Additionally, the gel times for the two systems are nearly identical.) Condensation has proceeded rapidly to give a distribution of condensed species typical of acid-catalyzed sols. H NMR spectra show rapid and nearly complete hydrolysis and the... 

A similar TEMPO-catalyzed system for the oxidation of alcohols using l-chloro-l,2-benziodoxol-3(l//)-one (130) (Section 2.1.8.1.1) as the terminal oxidant in ethyl acetate in the presence of pyridine at room temperature has been reported [158], Various alcohols 129 can be oxidized to the corresponding carbonyl compounds in high to excellent yields under these conditions (Scheme 3.55). The oxidation of primary alcohols (129, = H) in this reaction proceeds generally faster compared to the secondary alcohols. 

There are several examples of catalyzed aromatic cycloadditions leading to heterocyclic systems. The rhodium(II) acetate-catalyzed intramolecular Buchner reactions of iV-benzyldiazoacetamides 64a/b afford azabicyclo[5.3.0]decatrienes 66a/b in excellent yields. In contrast, the N-methyl derivative 64c gives 66c in moderate yield. Use of rhodium(II) perfluorobutyrate (Rh2(pfb)4) in place of rhodium(II) acetate increases the yield to 54%. Unlike its carbon counterpart, dihydroazulenone 29a (vide supra), 66a is insensitive to either trifluoroacetic acid or boron trifluoride etherate, even in excess, and the unrearranged reactant is recovered intact even after prolonged treatment at room temperature. 

In contrast to oxidation in water, it has been found that 1-alkenes are directly oxidized with molecular oxygen in anhydrous, aprotic solvents, when a catalyst system of PdCl2(MeCN)2 and CuCl is used together with HMPA. In the absence of HMPA, no reaction takes place(100]. In the oxidation of 1-decene, the Oj uptake correlates with the amount of 2-decanone formed, and up to 0.5 mol of O2 is consumed for the production of 1 mol of the ketone. This result shows that both O atoms of molecular oxygen are incorporated into the product, and a bimetallic Pd(II) hydroperoxide coupled with a Cu salt is involved in oxidation of this type, and that the well known redox catalysis of PdXi and CuX is not always operalive[10 ]. The oxidation under anhydrous conditions is unique in terms of the regioselective formation of aldehyde 59 from X-allyl-A -methylbenzamide (58), whereas the use of aqueous DME results in the predominant formation of the methyl ketone 60. Similar results are obtained with allylic acetates and allylic carbonates[102]. The complete reversal of the regioselectivity in PdCli-catalyzed oxidation of alkenes is remarkable. 

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