Nozaki catalytic

S. Sato, M. Toita, T. Sodesawa, and F. Nozaki, Catalytic and acidicproperties of silica-alumina prepared by chemical vapor deposition . Applied Catal. A, 62, 73-84 (1990). 

Catalytic, enantioselective cyclopropanation enjoys the unique distinction of being the first example of asymmetric catalysis with a transition metal complex. The landmark 1966 report by Nozaki et al. [1] of decomposition of ethyl diazoacetate 3 with a chiral copper (II) salicylamine complex 1 (Scheme 3.1) in the presence of styrene gave birth to a field of endeavor which still today represents one of the major enterprises in chemistry. In view of the enormous growth in the field of asymmetric catalysis over the past four decades, it is somewhat ironic that significant advances in cyclopropanation have only emerged in the past ten years. 

From a historical perspective it is interesting to note that the Nozaki experiment was, in fact, a mechanistic probe to establish the intermediacy of a copper carbe-noid complex rather than an attempt to make enantiopure compounds for synthetic purposes. To achieve synthetically useful selectivities would require an extensive exploration of metals, ligands and reaction conditions along with a deeper understanding of the reaction mechanism. Modern methods for asymmetric cyclopropanation now encompass the use of countless metal complexes [2], but for the most part, the importance of diazoacetates as the carbenoid precursors still dominates the design of new catalytic systems. Highly effective catalysts developed in... 

The catalytic asymmetric cyclopropanation of an alkene, a reaction which was studied as early as 1966 by Nozaki and Noyori,63 is used in a commercial synthesis of ethyl (+)-(lS)-2,2-dimethylcyclo-propanecarboxylate (18) by the Sumitomo Chemical Company (see Scheme 5).64 In Aratani s Sumitomo Process, ethyl diazoacetate is decomposed in the presence of isobutene (16) and a catalytic amount of the dimeric chiral copper complex 17. Compound 18, produced in 92 % ee, is a key intermediate in Merck s commercial synthesis of cilastatin (19). The latter compound is a reversible... 

Catalytic turn-over [59,60] in McMurry couplings [61], Nozaki-Hiyama reactions [62,63], and pinacol couplings [64,65] has been reported by Fiirst-ner and by Hirao by in situ silylation of titanium, chromium and vanadium oxo species with McaSiCl. In the epoxide-opening reactions, protonation can be employed for mediating catalytic turn-over instead of silylation because the intermediate radicals are stable toward protic conditions. The amount of Cp2TiCl needed for achieving isolated yields similar to the stoichiometric process can be reduced to 1-10 mol% by using 2,4,6-collidine hydrochloride or 2,6-lutidine hydrochloride as the acid and Zn or Mn dust as the reduc-tant (Scheme 9) [66,67]. 

Nozaki K, Ojima I (2000) Asymmetric carbonylation. In Ojima I (ed) Catalytic asymmetric synthesis. Wiley-VCH, New York, p 429... 

Nozaki-Hiyama-Kishi (NHK) reactions215,216 are well known and often employed as a useful method for the synthesis of natural products by coupling of allyl, alkenyl, alkynyl, and aryl halides or triflates with aldehydes. The organochromium reagents are prepared from the corresponding halides or triflates and chromium(ll) chloride, and are employed in polar aprotic solvents (THF, DMF, DMSO, etc.). Subsequently, it was found that nickel salts exhibited a significant catalytic effect on the formation of the C-Cr bond217,218 (Equation (19)). 

Certain transition metal complexes catalyze the decomposition of diazo compounds. The metal-bonded carbene intermediates behave differently from the free species generated via photolysis or thermolysis of the corresponding carbene precursor. The first catalytic asymmetric cyclopropanation reaction was reported in 1966 when Nozaki et al.93 showed that the cyclopropane compound trans- 182 was obtained as the major product from the cyclopropanation of styrene with diazoacetate with an ee value of 6% (Scheme 5-56). This reaction was effected by a copper(II) complex 181 that bears a salicyladimine ligand. 

Solutions to similar problems of achieving catalytic turnover [22] in McMurry couplings [23], Nozaki—Hiyama reactions [24], and pinacol couplings [25] have been reported by Fiirstner and by Hirao. The key step in these reactions is the in situ silylation of titanium and vanadium oxo species with Me3SiCl and reduction of the metal halides by suitable metal powders, e. g. zinc and manganese dust, as shown in Scheme 12.13. 

Scheme 12.14. Cozzi s catalytic enantio-selective Nozaki—Hiyama reaction.

Alternating insertions. The reaction proceeds via a perfectly alternating sequence of carbon monoxide and alkene insertions in palladium-carbon bonds (Figure 12.1). Several workers have shown the successive, stepwise insertion of alkenes and CO in an alternating fashion. In catalytic studies this was demonstrated by Sen, Nozaki, and Drent etc. In particular the work of Brookhart [15,22] and Vrieze/van Leeuwen [12,13,14,20,23,32] is relevant for stepwise mechanistic studies. The analysis of final polymers shows that also in the final product a perfect alternation is obtained. It is surprising that in spite of the thermodynamic advantage of alkene insertion versus CO insertion nevertheless exactly 50% of CO is built in. 

For recent reviews of catalytic Nozaki-Hiyama coupling, see [258-261]. 

Nozaki, K. In Catalytic Synthesis of Alkene-Carbon Monoxide Copolymerrs and Cooligomers, Chap. 7, Sen, A. (Ed.), Kluwer Academic Publishers, Dordrecht, 2003. 

Usanov and Yamamoto recently found that catalytic amounts of Co(TPP) 367 led to a dramatic rate acceleration of Nozaki-Kishi-Hiyama reactions catalyzed by chromium complex 368 (Fig. 101) [460]. The authors attributed the rate enhancement to initial reduction of 367 to a Co(I) complex. The latter is able to undergo an Sn2 substitution at propargyl bromide 366 giving an allenylCo(ffl) species. It was proposed that its homolysis leads to allenyl radical 366A, which couples to Cr(II) complex 368. The resulting allenyl Cr(III) complex adds in an SN2 process... 

Intramolecular Nozaki reaction. The addition of a vinyl-chromium compound to an aldehyde (12, 137 14, 96) is useful for macrocyclization, particularly if the CrCl2 reagent is activated by a catalytic amount of Ni(acac)2. Under these conditions, the vinyl iodide with a w-formyl group (1) cyclizes to (+ )-brefeldin C 12) and the 4-epimer as a 1 4 mixture in 60% yield.1... 

Chromium. Similar chlorosilane-mediated catalytic processes can be envisaged with many other early transition metals. The development of the first Nozaki-Hiyama-Kishi reactions catalyzed by chromium species [13] illustrates how to avoid the use of an excess of a physiologically suspect and rather expensive salt without compromising the efficiency, practicality and scope of the reaction. The tentative catalytic cycle is depicted in Scheme 3. 

In this case, the silylation of the metal alkoxide initially formed represents the key step of the overall process which releases the chromium salt from the organic product. The other crucial parameter is the use of the stoichiometric reducing agent for the regeneration of the active Cr" species. Commercial Mn turned out to be particularly well suited, as it is very cheap, its salts are essentially non-toxic and rather weak Lewis acids, and the electrochemical data suggest that it will form an efficient redox couple with Cr . Moreover, the very low propensity of commercial Mn to insert on its own into organic halides guarantees that the system does not deviate from the desired chemo- and diastereoselective chromium path. Thus, a mixture of CrX ( = 2, 3) cat., TMSCl and Mn accounts for the first Nozaki reactions catalytic in chromium [13]. 

This method applies to aryl, alkenyl, allyl and alkynyl halides as well as to alkenyl Inflates and exhibits the same selectivity profile as its stoichiometric precedent (Scheme 4). Moreover, it does not matter if the catalytic cycle is started at the Cr or Cr " stage as implied by Scheme 3. Therefore it is possible to substitute cheap and stable CrClj for the expensive and air-sensitive CrCf previously used for Nozaki reactions. In some cases other chromium templates such as [Cp2Cr or [CpCrCl2] can be employed, improving the total turnover number of this transformation even further [13, 14]. 

Scheme 3. Proposed catalytic cycle for the first Nozaki-Hiyama-Kishi reactions catalyzed by chromium species.

For recent applications of this multicomponent system to other Nozaki-Hiyama-Kishi reactions catalytic in chromium see a) With acrolein acetals R. K. Boeckman, R. A. Hudack, J. Org. Chem. 1998, 63, 3524-3525 b) With trichloroethane J. R. Falek, D. K. Barma, C. Mioskowski, T. Sehlama, Tetrahedron Lett. 1999, 40, 2091-2094 e) CrC cat., TMSCl, NiClj cat., Al-powder M. Kuro-boshi, M. Tanaka, S. Kishimoto, K. Goto, H. Tanaka, S. Torii, Tetrahedron Lett. 1999,40,2785 - 2788. 

Oshima and Nozaki generated the aluminum enolate regiospecifically by treatment of a-halo carbonyl compounds with Bu3SnAlEt2 subsequent reaction with aldehydes or ketones under mild conditions gave /3-hydroxy carbonyl compounds [117]. This subsequent aldol reaction is accelerated by the addition of catalytic Pd(PPh3)4 (Sch. 81). 

Nozaki F, Ohki K (1972) A study of catalysis by uranium oxide and its mixed catalysis, 3. Comparison of uranium oxide catalysts with vanadium oxide, molybdenum oxide and tungsten oxide catalysts for catalytic oxidation of carbon monoxide. Bull Chem Soc Jap 45 9473... 

Many catalytic reactions are not sensitive to the presence of a sulfur atom on the substrate. Two examples can be quoted the Nozaki-Hiyama-Kishi reaction where a chlorosilane-mediated Cr-Mn-catalyzed C-C coupling occurs between a halogenoalkene and an aldehyde [63], and the [IrCl(CO)3]-catalyzed intramolecular allyl transfer in functionalized 1,3-thiozanes [64]. 

Furstner, A., Shi, N. Nozaki-Hiyama-Kishi Reactions Catalytic in Chromium. J. Am. Chem. Soc. 1996, 118, 12349-12357. 

Bandini, M., Cozzi, P. G., Melchiorre, P., Umani-Ronchi, A. The first catalytic enantioselective Nozaki-Hiyama reaction. Angew. Chem., Int. Ed. Engl. 1999, 38, 3357-3359. 

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