Diazo compounds catalysts

Diazo compound Catalyst Conditions Ratio [diazo comp.]/ [catalyst]... 

Entry Diazo compound Catalyst/ ligand Time/T (h/°C) ee (o/o)b Yield (%) Refs. 

The available literature data support the assertion that the outcome of the methylene cycloadditions depends to a large extent on the ability of the olefin to be coordinated to the palladium center. In that respect, the mechanism of palladium-catalyzed cyclopropanation appears to differ significantly from that of rho-dium(ll)-catalyzed cyclopropanations. One advantage of using palladium catalysts with diazomethane is associated with the possibility of synthesizing polycyclopropane adducts, a topic of current interest (vide infra) which has no general satisfactory solution with other diazo compound/catalyst combinations. This point is exemplified below for the cyclopropanation of the esters of trans-polyunsaturated acids. Moreover, the reactivity of the double bonds depends both on their position in the linear hydrocarbon chain and on their configuration (eq. (f)). 

Diene 16 Diazo Compound Catalyst Solvent " Product 18 Ref... 

Typically, the diazo compound catalyst molar ratio is (300-1000) 1. 

Diazo Compound Catalyst Carbene Alkene Cyclopropane Ratio (cis Ivans) Yield (%) Ref... 

Cyclization of the diazo compound (108) with a copper catalyst affords the clavulanic acid derivatives (110) and (111), possibly via rearrangement of the sulfur ylide (109) (80H(14)1999). Similar reactions have been reported in the recent literature (80H(14)1967, 81H(16)1305, 80TL31). 

Ring enlargement of benzene derivatives by carbenes generated from diazo compounds (better in the presence of a Rh catalyst) Conversion of aldehydes to ketones by diazo compounds (Schlotterbeck) see also Ptau Planer... 

Gothelf presents in Chapter 6 a comprehensive review of metal-catalyzed 1,3-di-polar cycloaddition reactions, with the focus on the properties of different chiral Lewis-acid complexes. The general properties of a chiral aqua complex are presented in the next chapter by Kanamasa, who focuses on 1,3-dipolar cycloaddition reactions of nitrones, nitronates, and diazo compounds. The use of this complex as a highly efficient catalyst for carbo-Diels-Alder reactions and conjugate additions is also described. 

The mechanism through which catalytic metal carbene reactions occur is outlined in Scheme 2. With dirhodium(II) catalysts the open axial coordination site on each rhodium serves as the Lewis acid center that undergoes electrophilic addition to the diazo compound. Lewis bases that can occupy the axial coor-... 

The use of dirhodium(II) catalysts for catalytic reactions with diazo compounds was initiated by Ph. Teyssie [14] in the 1970s and rapidly spread to other laboratories [1]. The first uses were with dirhodium(II) tetraacetate and the more soluble tetraoctanoate, Rh2(oct)4 [15]. Rhodium acetate, revealed to have the paddle wheel structure and exist with a Rh-Rh single bond [16], was conve-... 

The reaction of diazo compounds with amines is similar to 10-15. The acidity of amines is not great enough for the reaction to proceed without a catalyst, but BF3, which converts the amine to the F3B-NHR2 complex, enables the reaction to take place. Cuprous cyanide can also be used as a catalyst. The most common substrate is diazomethane, in which case this is a method for the methylation of amines. Ammonia has been used as the amine but, as in the case of 10-44, mixtures of primary, secondary, and tertiary amines are obtained. Primary aliphatic amines give mixtures of secondary and tertiary amines. Secondary amines give successful alkylation. Primary aromatic amines also give the reaction, but diaryl or arylalkyl-amines react very poorly. 

Since their first introduction by Brunner and McKervey as chiral catalysts for the asymmetric cyclopropanation of alkenes with diazo compounds, chiral dirhodium tetra(A-arylsulfonylprolinates) complexes have been widely used by Davies,in particular, in the context of these reactions. Therefore, the use of... 

Metal-Catalyzed. Cyclopropanation. Carbene addition reactions can be catalyzed by several transition metal complexes. Most of the synthetic work has been done using copper or rhodium complexes and we focus on these. The copper-catalyzed decomposition of diazo compounds is a useful reaction for formation of substituted cyclopropanes.188 The reaction has been carried out with several copper salts,189 and both Cu(I) and Cu(II) triflate are useful.190 Several Cu(II)salen complexes, such as the (V-f-butyl derivative, which is called Cu(TBS)2, have become popular catalysts.191... 

The synthetic utility of the ring expansion reaction was demonstrated by its application to the synthesis of thermolabile thiepins. When the diazo compound (66) obtained from benzo[c]thiopyrylium salt 65 was treated with palladium catalyst under the same conditions as in the case of 63, the product isolated was ethyl 2-naphthoate (68)48). The plausible reaction pathway is one comprising i) decomposition of 66 to the corresponding carbene intermediate, ii) ring expansion to the... 

Besides the formation of carbenes from diazo compounds and the hydroformyla-tion, rhodium (as described previously for palladium) has also been used as catalyst in domino processes involving cycloadditions. Thus, Evans and coworkers developed a new Rh(I)-catalyzed [4+2+2] cycloaddition for the synthesis of eight-membered rings as 6/2-105 using a lithium salt of N-tosylpropargylamines as 6/2-104, allyl carbonates and 1,3-butadiene (Scheme 6/2.22) [221]. The first step is an al-... 

Diazo compounds 107 were heated to reflux in the presence of a rhodium catalyst giving rise to the carbene followed by intramolecular cyclization to give the diastereomeric pairs of ylides 5 and 108 (Equation 22) <2006T1459>. 

The same difference in regioselectivity holds for cyclopropanation with ethyl diazoacetate 25 K It is assumed that Cu(OTf)2 or Cu(BF4)2 are reduced to the Cu(I) salts by the diazo compound the ability of CuOTf to form stable complexes with olefins may then explain why, with these catalysts, cyclopropanation is governed by the steric environment around a double bond rather than by its electron-richness. 

For many catalytic cyclopropanations, the stereoselectivity describing the stereochemical relation between substituents at the carbenoid and those at the double bond is not very pronounced. EjZ or syn/anti ratios of ca. 1-3 in favor of the less congested isomer may be considered normal (for examples see Tables 6 and 7). The stereochemical outcome can be expected to be governed by the nature of the olefin, the diazo compound and the catalyst. 

Enantioselective carbenoid cyclopropanation can be expected to occur when either an olefin bearing a chiral substituent, or such a diazo compound or a chiral catalyst is present. Only the latter alternative has been widely applied in practice. All efficient chiral catalysts which are known at present are copper or cobalt(II) chelates, whereas palladium complexes 86) proved to be uneflective. The carbenoid reactions between alkyl diazoacetates and styrene or 1,1 -diphenylethylene (Scheme 27) are usually chosen to test the efficiency of a chiral catalyst. As will be seen in the following, the extent to which optical induction is brought about by enantioselection either at a prochiral olefin or at a prochiral carbenoid center, varies widely with the chiral catalyst used. 

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