Alkylcopper complexes

TRISUBSTITUTED ALKENES FROM ADDITION OF GRIGNARD-DERIVED ALKYLCOPPER COMPLEXES TO ACETYLENES,... 

Conjugate addition.s The key step in a stereocontrolled synthesis of the Lyth-raceae alkaloid lasubine II (4) is the conjugate addition of an alkylcopper complexed with BF3 to the N-acyl-2,3-dihydro-4-pyridone 1 to give the d.v-product 2 in 56% yield and >96% stereoselectivity. Hydrogenation in the presence of Li2C03 effects cyclization and deprotection of nitrogen to give the ketone 3, which is reduced stereoselectively by lithium trisiamylborohydride to the desired alcohol 4. 

Trtsubstitutedalkenes. Complete details have been published for preparation of these alkenes by addition of alkylcopper complexes to acetylenes. The paper includes numerous references to work of other laboratories as well, The paper also presents convincing evidence that the reaction involves xyn-addition with a high degree of stereoselectivity. ... 

The conjugate addition of Grignard reagents to 2-cyclohexenone was promoted by catalytic amounts (2-4 mol %) of alkylcopper(I) complexes of the lithium amide prepared from N- (R)-1 -phenylethyl]-2-[(/ )-l-phenylethyliminojcycloheptatrienamine, Li[CuR(CHIRAMT)]52,11. However, 3-substituted cyclohexanones were obtained in very low ee (4-14%). 

In a parallel study, Wipf and Fritch11041 have shown that also urethane-protected (Boc), and even amino acid segments, are tolerated as acyl compounds on the aziridine nitrogen. The best results were obtained with alkylcopper reagents derived from CuCN and an alkyl-lithium in the presence of boron trifluoride-diethyl ether complex. Some 6-alkylated compounds (11-15%) were isolated as well. This work was extended to a solid-phase procedure that resulted in resin-bound alkene isosteres that could immediately be used in further peptide synthesis.11051 For this purpose, the 2-nitrophenylsulfonyl (oNbs) group was used for nitrogen protection and aziridine activation. It could be readily cleaved with benzenethio-late, which was compatible with the acid-sensitive Wang linker used. 

Highly stereoselective cis additions of organocuprates to alkynic esters have also been reported with alkylcopper-Lewis acid complexes.3 The choice of the proper Lewis acid was found to be important in determining the stereoselection as was demonstrated with enyne (32 Table 2).5- 8 While both the diorga-nocuprate and the alkylcopper-BF3 complex gave mixtures of stereoisomers, the Bu u-BEts provided... 

When terminal alkynes are used as substrates, alkylcoppermagnesium dihalides prepared from a cop-peril) bromide-dimethyl sulfide complex typically are used (e.g. equation 31134 and Scheme 7).135 The choice of a Grignard reagent, from which the alkylcopper(I) species is prepared, is important in this instance, alkyllithium-derived alkylcopper reagents usually are less satisfactory.10... 

All these reactions proceed by initial base-promoted formation of copper amide complexes 306A from diarylamines or sulfonamides 306 or 308, respectively, which are subject to a concerted, sv -amidocupration with the adjacent alkene unit via transition state 306B (Fig. 82). The resulting alkylcopper(II) intermediates 306C are... 

The high-temperature pyrolysis of dry copper(II) heptafluoropro-pionate afforded only traces of 3 6, C3F 7COF, and unidentified products 183). Such decarboxylations are worthy of reinvestigation in strong complexing solvents as a possible route to the stable perfluoro-alkylcopper compounds (see Section II,E). 

Formation of metal-carbon bonds by addition of an organometallic reagent to an unsaturated compound or a diazonium compound is a little-used method in organocopper chemistry. Various alkylcopper reagents, (RCu + MgXg or LiX), add to acetylene or the alkynes, RC=CH, in a cis manner in ether or ether-pentane at low temperatures (223). A 7T-complex is a probable intermediate. The vinylcopper addition product obtained is dependent on the nature of the alkyne, being sensitive to electronic effects in the latter ... 

Alkylcopper compounds are more stable in THF than in ether solutions, even with the help of phosphine ligands, because of the ability of THF to form more stable complexes (283). A paramagnetic species was not detected in ether solution. 

Alkanoic acids or their copper salts cannot be decarboxylated under the same conditions as those acids which contain a rr-system (56), although fluorene-9-carboxylic acid appears to be an exception 279). 9-Fluo-renylcopper is the supposed intermediate. Under certain conditions the decarboxylation of alkanoic acids by lead(IV) is catalyzed by copper(II) complexes alkylcopper species have been proposed as intermediates 179). 

The redox reactions of carbon free radicals and copper(II) compounds have been portrayed as ligand-transfer and electron-transfer processes 178). The electron-transfer oxidation of alkyl radicals by copper(II) complexes, which are efficient radical interceptors, is considered to proceed via a metastable alkylcopper species which is consumed primarily by oxidative elimination [Eq. (129)] and oxidative solvolysis [Eq. (130)] 143b). The anionic counterion exerts a dominant effect in the selection... 

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