Lower order cuprates

The use of stannylcuprate reagents is well established.112,113 The reactions occur under mild conditions. They are reversible, and the reactivity and regio- and stereo-selectivity are sensitive to the structure and reaction conditions, as illustrated by the reaction of allene with the lower-order cuprate Bu3SnCuCNLi and, more readily, with the higher order cuprate (Bu3Sn)2CuCNLi (Equation (29)).114... 

The use of a 2-thienyl group as a nontransferable ligand in lower order cuprates has been described, H. Malmberg, M. Nilsson and C. Ullenius, Tetrahedron Lett., 1982, 23, 3823. 

Ligands containing sulfur attached directly to copper in mixed lower order cuprates have been preferentially transferred (a) T. G. Back, S. Collins and K. W. Law, Tetrahedron Lett., 1984, 25, 1689 (b) E. Piers, K. F. Cheng and 1. Nagakura, Can. J. Chem., 1982, 60, 1256. 

Although lower-order cuprate reagents will often engage in displacement reactions with alkyl halides, such reactions are usually slow. They are generally much less facile than 1,4-addition reactions to a,P-unsaturated enones or enoates. The latter processes are particularly facile when trimethylsilyl chloride is employed as an additive. It was Corey and Boaz10 who first recognised the accelerating effect of trimethylsilyl chloride on cuprate addition reactions to a,p-unsaturated carbonyls. Buszek therefore capitalised on Corey s earlier observations in his reaction of 10 with lithium dimethylcuprate to obtain 15. 

The reagent transfers the trimethyltin group to the (3-position of a variety of a,p-unsaturated esters, including acetylenic esters. It is generally superior to the lower-order cuprate [(CH3)3SnCuSC6H5]Li (10, 289). 

Most of the recent developments in the vinyl halide reaction chemistry of lower-order cuprates are of zinc cyanocuprates (RCu(CN)ZnX)24. While only reacting with unfunc-... 

The reaction of allyl halides with organocopper species usually gives regiochemical mixture of direct and S 2 attack. Exceptions to this trend are 3,3-disubstituted 1-bro-moalkenes, which give reliable direct substitution with lower-order cuprates or RCu organocopper reagents. This fact has been put to use in the synthesis of several prenelated... 

LO cuprate = A lower order cuprate HO cuprate = A higher order cuprate Rr = A residual or nontransferable ligand R/ = A transferable hgand hfa = Hexafluoroacetylacetone acac = Acetylacetonate EWG = Electron-withdrawing group TfO = Trifluoromethylsulfonyloxy (triflate). 

Additions of nucleophiles to vinyl aziridines provide the issue of selectivity of 1,2 (Sn2) or 1,4 (Sn2 ) additions. During a very short efficient synthesis of pancratistatin, Hudlicky et al. chose to open a vinylaziridine 156 with an aromatic cuprate 157 <1996JA10752>. Formation of the trans-, Z adduct 158 was accomplished in 75% chemical yield (Equation 42). They found that the addition of simple lower order cuprates or Grignard reagents (aliphatic or aromatic) reacted to give the syn-, A addition, whereas higher-order cuprates gave the trans-, Z product. 

For aldehydes which lack a-heteroatoms and hence have no avenue for stereocontrol via chelation, enhanced Cram selectivity beyond that normally seen with lower order cuprates (i.e. 3 1 to 7 1 ) can be... 

A deacylation reaction has been effected by a reactive lower order cuprate when its reaction paitner has no other pathway available. Thus, Kunieda and Hirobe have found that (-)-3-ketopinyl-2-oxazolone (85) undergoes smooth cleavage of the chiral auxiliary to a ord the heterocycle (86), subsequent elaboration of which leads to either (2S,3/ )-3-hydroxyglutamic acid (87) or (3f ,4 )-4-amino-3-hydroxy-6-methylheptanoic acid (88) as their hydrochloride salts (Scheme 15). ... 

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