Catalysis sequential

Solinas M, Jiang J, Stelzer O et al (2005) A cartridge system for organometallic catalysis sequential catalysis and separation using supercritical carbon dioxide to switch phases. Angew Chem Int Ed 44(15)2291-2295... 

However, the latter type of metal-catalyzed cascade reactions turns out to be even more challenging since issues of selectivity and efficiency are crucially dependent on the particular catalyst structure. This type can either be performed in a parallel or sequential fashion [16,21], Whereas parallel catalysis is significantly more difficult to develop, sequential catalysis offers the possibility of altering reaction conditions and additives from step to step in the sense of bi- or multicatalytic one-pot processes, assisted tandem catalysis, or auto tandem catalysis [1]. Therefore, a demanding goal is the development of one-catalyst multireaction sequences that set the stage for new reactions in diversity-oriented syntheses of complex molecular structures (for reviews on diversity-oriented syntheses see [27-33]). 

A completely different mode of applying the Sonogashira coupling for sequential catalysis can be envisioned by introduction of further steps that are not catalyzed by transition metals. Here, Muller and coworkers [114] have just recently demonstrated that acid chlorides 156 and terminal propargyl THP ethers 157 after Sonogashira coupling can be transformed in a one-pot fashion into iodo furans 158 in moderate to good yields (Scheme 60). 

Another option for Sonogashira coupling as an initiator of sequential catalysis is the coupling isomerization reaction (CIR) of electron-deficient halide and 1-aryl propargyl alcohols giving rise to the formation of chalcones [115, 116]. Based upon the CIR of electron-deficient halides 163 and l-(p-bromo phenyl) propyn-l-ol (164) Muller and Braun [117] presented a consecutive... 

The first two carbinolamlnes named were synthesized using sequential catalysis by cytochrome P-450 oxygenase and glucuronyl transferase inmobllized from rabbit liver microsomes onto sepharose beads (64,65) as shown in scheme 3. 2-Pra1 idoxime chloride was allowed to decompose at pH 7.4 in the presence of immobilized UDP-glucuronyl transferase and the cofactor uridine... 

Ackermann L, Bom R, Alvarez-Bercedo P (2007) Ruthenium(IV) alkylidenes as precatalysts for direct arylations of alkenes with aryl chlorides and an application to sequential catalysis. Angew Chem Int Ed 46 6364-6367... 

Meanwhile, an efficient procedure for the sequential catalysis of olefin cross-metathesis and AFC alkylation was developed (Scheme 6.58). Two distinct catalytic processes were involved in this procedure, olefin crossmetathesis of 135 and 136 catalyzed by a Ru complex and intramolecular AFC alkylation catalyzed by a chiral phosphoric acid. In the presence of 5 mol% Ru complex and 5 mol% chiral phosphoric acid (S )-13b, the reaction of indolyl allyl ether or amine 135 and phenyl enone 136 proceeded smoothly to afford the desired products 134 in good to excellent yields (43-97%) with good enantioselectivity (80-94% ee). 

The slightly decreased enantioselectivity observed during sequential catalysis was likely due to the formation of racemic product induced by the Ru complex. Notably, the AFC reaction facilitated the cross-metathesis reaction by converting the metathesis product into an alkylation product to drive the equilibrium of the metathesis reaction, as supported by the observation that the cross-metathesis reaction between 135 and 136 led to 133 in only moderate yield in the absence of chiral phosphoric acid. 

The above-described protocol can also be employed in the synthesis of propargyl substituted propiolates. These reactive intermediates can be transformed in a CuAAC to yield 1,2,3-triazolylmethyl arylpropiolates 56 in a one-pot fashion applying the concept of sequential catalysis in generally excellent yields considering the formation of four new bonds and a bondforming efficiency of 73—87%. It is noteworthy that the CuAAC... 

As 1,4-disubstituted 1,2,3-triazoles are usually prepared through copper-catalyzed 1,3-dipolar cycloadditions of terminal alkynes with organic azides, the use of a single copper complex for a direct arylation-based sequential catalysis was probed. Thereby, a modular chemo- and regioselective synthesis of fully-substituted 1,2,3-triazoles was achieved (Scheme 9.43). Notably, the overall reaction involved the selective coupUng of four components through the formation of one C—C- and three C—N-bonds [58]. 

Mast N, Annalora AJ, Lodowski DT, Palczewski K, Stout CD, Pikuleva IA (2011) Structural basis for three-step sequential catalysis by the cholesterol side chain cleavage enzyme CYPllAl. J Biol Chem 286 5607-5613... 

This reaction represents the first example of a sequential catalysis leading to 2-oxazolidinones derivatives starting from acyclic precursors (140). 

Martin et al. [199] illustrated the concept of sequential catalysis by the development of the first cascade sequences involving Rh-catalyzed allyhc alkylation/[5+2j-cycloaddition and allylic alkylation/cycloisomerization (Scheme 12.95). The method was also applicable to a cascade allylic alkylation/Pauson-Khand annelation that nicely complements existing procedures. The ability to exploit multifunctional... 

Scheme 26.1 Cooperative (or synergistic), relay, and sequential catalysis (S.M., starting materials INT., intermediaries P., products CAT, catalyst).

Sequential Catalysis. This is a one-pot process in which one of the catalysts is added in the course of the reaction to avoid self-quenching. 

Sequential Catalysis Involving Metal-Catalyzed Cycloisomerizations and Cyclizations... 

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