Copper pivalate

The oxidative coupling of benzothiazoles with azine JV-oxides is promoted by catalytic Pd(OAc)2 and CuBr and stoichiometric Cu(OPiv)2 (eq 142). The copper pivalate salt plays a dual role oxidant and concerted metalation-deprotonation (CMD) promoter, while the role of copper bromide is less obvious. 

Rhodium(II) pivalate has also been recommended for the cyclopropanation of vinyl halides with ethyl diazoacetate 78). As Table 8 shows, yields with this catalyst are far higher and reaction conditions milder than with copper. Failures are noted,... 

Table 8. Cyclopropanation of vinyl halides with ethyl diazoacetate in the presence of rhodium(Il) pivalate (Rhpiv) or copper...

The search for catalysts which are able to reverse the ratio of cyclopropane diastereomers in favor of the thermodynamically less stable isomer has met with only moderate success to date. Rh(II) pivalate and some ring-substituted Rh(II) benzoates induce cw-selectivity in the production of permethric acid esters 77,98 99 contrary to rhodium(II) acetate, which gives a 1 1 mixture 74,77,98), and some copper catalysts 98) (Scheme 10). 

Similar to the intramolecular insertion into an unactivated C—H bond, the intermolecular version of this reaction meets with greatly improved yields when rhodium carbenes are involved. For the insertion of an alkoxycarbonylcarbene fragment into C—H bonds of acyclic alkanes and cycloalkanes, rhodium(II) perfluorocarb-oxylates 286), rhodium(II) pivalate or some other carboxylates 287,288 and rhodium-(III) porphyrins 287 > proved to be well suited (Tables 19 and 20). In the era of copper catalysts, this reaction type ranked as a quite uncommon process 14), mainly because the yields were low, even in the absence of other functional groups in the substrate which would be more susceptible to carbenoid attack. For example, CuS04(CuCl)-catalyzed decomposition of ethyl diazoacetate in a large excess of cyclohexane was reported to give 24% (15%) of C/H insertion, but 40% (61 %) of the two carbene dimers 289). 

Parameter Copper tetra-phenylporphin Copper tetra-phenyl(pival-amido) porphin Tetramethyl ether of copper hemato-IX porphyrin... 

Cyclopropanation. Rhodium(II) pivalate is superior to copper catalysts for the cyclopropanation of l,l-dihalo-4-methylpenta-l,3-dienes (1) with ethyl diazoacetate. The yield is higher than that obtained with copper catalysts (48%), and the cis/trans ratio is considerably higher. Similar contrathermodynamic product ratios were observed with other substrates. 

Arylation of amines. Rapid transfer of an aryl group from ArjBifOAclj to amines is catalyzed by copper(II) pivalate (9 examples, 45-100%). 

Aldehyde 126 was converted to the terminal alkyne (142) in 61% yield by Seyferth-Gilbert homologation (Scheme 23) [60]. These basic conditions were well tolerated and no C-8 epimerization or C-2 deacetylation was observed. Alkyne 142 was coupled with various azides under copper(I)-catalyzed click reaction conditions to afford 1,4-disubstituted-l,2,3-triazoles (143-145) in 88% yield. Similar conditions were used to generate unsubstituted 1,2,3-triazoles. Alkyne 142 was coupled to azidomethyl pivalate under click reaction conditions to give the pivalyl triazole (146) in 88% yield. The pivalyl triazole was then treated with IN NaOH to remove both the pivalyl group and the C-2 acetyl group. These conditions also led to C-8 epimerization. Acetylation of the epimeric mixture under standard conditions (AC2O, pyridine) and preparative scale separation by TLC furnished the C-8 epimeric N-unsubstituted triazoles (147) in 54% yield over three steps in a ratio of 4 6 (C-8 epi-C-8). 

The copper-mediated O-alkylation of alcohols with It, I i affords a mixture of alkyl ethers and aldehydes derived from the R group [286]. Dimethyl malate can be O-phenylated by combined use of PhsBi and OXONE in the presence of copper(II) pivalate (Scheme 14.138) [287]. The 0-phenylation of phenols with PhjBi proceeds smoothly in the presence of Cu(OAc)2 and EtjN [281a]. 

Imidazole /V-oxide substrates may be used in a similar fashion. Initial investigations revealed that the use of palladium acetate in conjunction with an electron deficient 4-fluorophenylphosphine in acetonitrile at 70 °C provides C2 arylation in high yields. With the goal of achieving the same reactivity at or near room temperature it was determined that the use of palladium acetate in conjunction with a Buchwald ligand, catalytic copper bromide and 30 mol% pivalic acid in acetonitrile could also achieve high yields of C2 arylation at 25 °C. As was the case with thiazole V-oxides. if the C2 and C5 positions of the imidazole are blocked C4 arylation may also be achieved in synthetically useful yield (Scheme 15). 

Both dimethylphenylphosphine-borane (107) and -sulfide (108) are enantio-selectively deprotonated by a lithiumalkyl (—)-sparteine complex as demonstrated by subsequent reaction with electrophiles to give products with e.e. values of 80-87% (Scheme 8). Oxidative coupling of (109) in the presence of copper(II) pivalate gives the (S. S)-isomer (110) as the major product. Asymmetric metalla-tion and silylation of diphenylphosphinyl ferrocene (111) using the chiral lithium amide base derived from di(l-methylbenzyl)amine has been reported to give an... 

Alkylation of the Uthium salt of TMSCHN2 (TMSC(Li)N2) gives a -trimethylsLlyl diazoalkanes which are useful for the preparation of vinylsilanes and acylsilanes. Decomposition of a-tri-methylsilyl diazoalkanes in the presence of a catalytic amount of Copper(I) Chloride gives mainly ( )-vinylsilanes (eq 12), while replacement of CuCl with rhodium(II) pivalate affords (Z)-vinylsilanes as the major products (eq 12). Oxidation of a-trimethylsilyl diazoalkanes with m-Chloroperbenzoic Acid in a two-phase system of benzene and phosphate buffer (pH 7.6) affords acylsilanes (a-keto silanes) (eq 12). ... 

Reaction of copper(II) pivalate with sodium methoxide in ethanol (presumably a source of ethoxide not methoxide) produces a cyclic hexanuclear structure [Cu(02CCMe3)(0Et)]6. The Cu" Cu vectors are alternately bridged by two 1,3 carboxylates or two ethoxide oxygens. Magnetic studies show strong anti-ferromagnetic exchange between the Cu centers. 

Beifuss and his group developed a copper-catalyzed domino reaction to prepare 2-arylquinazolines from 2-bromobenzyl tosylates and benzamidine hydrochloride salts in the presence of copper(I) iodide (10mol%), potassium phosphate (3 equivalents), and pivalic acid (40mol%) in 1,2-dichlorobenzene... 

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