Copper hydride chiral

A highly enantioselective reduction of o /3-unsaturated nitriles has been conducted by using a Cu(OAc)2-josiphos complex as the catalyst under hydrosilylation conditions. This reaction provides access to valuable /3-aryl-substituted chiral nitriles in good yields and with excellent enantioselectivities by employing a stable catalytic pre- cursor and a readily available commercial bisphosphine ligand. The active reducing species is believed to be copper hydride.315... 

Asymmetric reduction of a, /I-unsaturated esters, lactones or lactames can be effected with copper-hydride catalysts and chiral phosphanes such as various BINAP related compounds in excellent yields and enantioselectivities (equation 23). As the hydrosilane component, polymethylhydrosiloxane (PMHS) is frequently used for this reaction. 

Copper hydride species generated in situ from hydrophenylsilane and a CuF complex initiates reductive aldol reaction by forming copper enolates (rather than enol silyl ethers). For accomplising a chiral reaction the ferrocenyl ligand 73 is added. 

Copper-catalyzed systems have been developed that reduce ketones directly to silyl ethers. The reactions involve chiral biphenyl diphosphine type ligands and silane or siloxane hydride donors.187... 

In contrast to phenolic hydroxyl, benzylic hydroxyl is replaced by hydrogen very easily. In catalytic hydrogenation of aromatic aldehydes, ketones, acids and esters it is sometimes difficult to prevent the easy hydrogenolysis of the benzylic alcohols which result from the reduction of the above functions. A catalyst suitable for preventing hydrogenolysis of benzylic hydroxyl is platinized charcoal [28], Other catalysts, especially palladium on charcoal [619], palladium hydride [619], nickel [43], Raney nickel [619] and copper chromite [620], promote hydrogenolysis. In the case of chiral alcohols such as 2-phenyl-2-butanol hydrogenolysis took place with inversion over platinum and palladium, and with retention over Raney nickel (optical purities 59-66%) [619]. 

Pyrazine 168 underwent cross-coupling with propyne in the tri-o-tolylphosphine, and copper(l) iodide to provide 170. The isocyanate or methyl chloroformate and sodium hydride to give An isolated example of the synthesis of chiral pteridines from a (Scheme 33). 2-Isothiocyanatopyrazine-3-carboxylates have been isothiocyanatopyrazine-2-carboxylate 172 reacted with R)- —) provided the pteridine derivative 173 and uncyclized pyrazine with pyridine precursors afforded pyrido[2,3 Pytitnidines. 

In fact, the role of copper and oxygen in the Wacker Process is certainly more complicated than indicated in equations (151) and (152) and in Scheme 10, and could be similar to that previously discussed for the rhodium/copper-catalyzed ketonization of terminal alkenes. Hosokawa and coworkers have recently studied the Wacker-type asymmetric intramolecular oxidative cyclization of irons-2-(2-butenyl)phenol (132) by 02 in the presence of (+)-(3,2,10-i -pinene)palladium(II) acetate (133) and Cu(OAc)2 (equation 156).413 It has been shown that the chiral pinanyl ligand is retained by palladium throughout the reaction, and therefore it is suggested that the active catalyst consists of copper and palladium linked by an acetate bridge. The role of copper would be to act as an oxygen carrier capable of rapidly reoxidizing palladium hydride into a hydroperoxide species (equation 157).413 Such a process is also likely to occur in the palladium-catalyzed acetoxylation of alkenes (see Section 61.3.4.3). 

Oppolzer has developed a method of asymmetric synthesis based on the use of the chiral auxiliaries 39A and 39B derived respectively from (+ )-camphor [(+ )-40] and (- )-camphor [(- )-40]. Crotonylation of 39A gave the ester that was attacked by 4-methyl-3-pentenyllithium in the presence of copper iodide tributylphosphine and boron trifluoride from only one side of the molecule, the product 41 having the (S)-configuration (enantioselectivity 98.5%). The ester 42—similarly obtainable from 39B—was methylated under similar conditions, also yielding 41 with 92% enantioselectivity. (S)-Citronellic acid [(S)-36] or (S)-citronellol [(S)-33] were then obtained from 41 by the action of sodium hydroxide or lithium aluminum hydride (Scheme 6). Reduction of potassium... 

Yu and Luo et al. reported a catalytic enantioselective benzylic C(sp )-H functionalization of 207 via a [l,5]-hydride transfer/cyclization sequence with the chiral complex of copper(II) and side-armed bisoxazoline 209 as catalyst, which provided tetrahydronaphthalene derivatives 208 in moderate to high yield with up to 69 % ee (Scheme 79). 

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