Magnesium cuprate

In the area of allenic non-natural product chemistry, the synthesis of the [34]alle-nophane 14 (Scheme 2.4) is particularly noteworthy, with all four of its allenic bridges being formed through subsequent SN2 substitution reactions of propargylic acetates with a methyl magnesium cuprate [14] (see Section 2.5 for an alternative synthesis of macrocyclic allenes). 

Due to its reliability, the SN2 substitution is often used in applications which require the highly enantioselective formation of the allene for example, Brummond et al. [19g] prepared the yneallene 19 (a starting material for intramolecular allenic Pauson-Khand cycloadditions) through the anti-selective SN2 substitution of the chiral propargylic mesylate 18 with a suitable magnesium cuprate (Scheme 2.6). 

Scheme 2.10 Sn2 substitution of propargyl oxirane 27 with magnesium cuprates.

Most gratifyingly, these conditions are also applicable to functionalized magnesium reagents [33], as demonstrated by the formation of a-hydroxyallenes 31-34 from ds- or trans-27 and the corresponding magnesium cuprates bearing substituted aryl groups (Scheme 2.11) [31]. 

The functionalized dienic (Z)-telluride 218 on reaction with magnesium cuprates 219 gives the (it)-olefins 220 (Scheme 116).284... 

Ether solutions of magnesium cuprates undergo 1,4-additions to acetylenic phosphine oxides or sulfides, unlike organolithium reagents... 

A number of organocopper reagents reportedly exhibit Sn2 selectivity even when steric factors would appear to favor a-attack. Magnesium cuprates, in general, show greater propensity to undergo reaction... 

Stephan and coworkers have performed similar 1,4-additions of magnesium cuprates to A-enoylimidazolidinones derived from 1.131. After hydrolysis, p-bran-ched acids were obtained with a high enantioselectivity [1424],... 

Allyl copper compounds are formed in the reaction between magnesium cuprates and dienesThese complexes may be 7t-allyl or a-allyl. 

In acyclic systems, Mukaiyama and co-workers found that addition of chiral magnesium cuprate R(A )CuLi derived from 456 gave good asymmetric induction. 20 Lithium cuprates derived from 458,... 

A different approach to solving this problem is to attach a chiral auxiliary to the enone substrate. The auxiliary is a chiral material that is attached to an achiral substrate. The asymmetry of the auxiliary controls the selectivity of the reaction and is then removed in a separate chemical step. Posner studied the use of optically pure a-carbonyl-a, 3-ethylenic sulfoxides (465, see sec. 3.9.A.ii for the preparation of optically active sulfoxides)." 29 Conjugate addition of di-(2,2,-dimethylpropyl)magnesium cuprate to the chiral... 

J. Wicha, K. Mikami, Synthesis (2001) 145 (with magnesium cuprates) ... 

---