La 3/linked-BINOL complex

For Type II reactions also a variety of useful compounds can be synthesized by changing the combination of the starting materials. In the Michael reaction with cyclic enones, availability of the La-linked-BINOL complex broadened the scope of the Michael acceptor (Scheme 14). It should be noted that less reactive medium-ring-size cyclic enones (7-9membered ring size) underwent conjugate addition highly enantioselectively (up to > 99 % ee) [17]. 

Scheme14. Use of the La-linked-BINOL complex in the Michael reaction with cyclic enones.

La-linked-BINOL complex 23 was introduced as a stable, storable, and reuse-able asymmetric catalyst for the Michael reaction [120]. Optimization of the reaction between dibenzyl malonate and 2-cyclohexene-1-one in DME afforded the Michael adduct in 94% yield and >99% ee. The extraordinary versatility of LnLB catalyts is also documented in the highly efficient Michael addition of thiols to a,y9-unsaturated carbonyl compounds [121] and tandem Michael-aldol reactions [122]. 

Takita R, Ohshima T, Shibasaki M. Highly enantioselective catalytic Michael reaction of a-substituted malonates using La-linked-BINOL complex in the presence of HFIP (1,1,1,3,3,3-hexafluoroisopropanol). Tetrahedron Lett. 2002 43(26) 4661 665. 

In the catalytic asymmetric aza-Morita-Baylis-HiUman reaction using unactivated methyl acrylate, the combined use of a La(0- Pr)3/(5, 5 )-TMS-linked-BINOL complex with a catalytic amount of l,4-diazabicyclo[2.2.2]octane (DABCO) promoted the aza-Morita-Baylis-Hillman reaction of a broad range of A-diphenylphosphinoyl imines." ... 

In addition to the simple malonates, the La-O-linked-BINOL complex was also found to be effective for handling asymmetric Michael addition of various a-substituted malonates to cyclic enone. Under this catalyst system, the Michael adducts could be obtained in 55-86% yields with... 

TABLE 9.4. Michael Addition Catalyzed by Alkalimetal-free (J d )-La-0-linked-BINOL Complex... 

A typical procedure for the Michael addition catalyzed by ( 5,5 )-La-NMe-linked-BINOL complex 5,5 )-La-NMe-linked-BINOL complex To a stirred solution of (5,5)-NMe-linked-BINOL [212.9 mg, including 11.6wt/wt% solvent (THF and hexane), O.SOmmol] in THF (1.95mL) at —78°C was added a solution of La(0-i-Pr)3 (1.5mL, O.SOmmol, 0.2M in THF, freshly prepared from the powder of La(0-i-Pr)3 and dry THF). The solution was stirred for 2.5 hours at room temperature, and then the solvent was evaporated under reduced pressure. The resulting residue was dried for 2 hours under reduced pressure (ca. 4 mmHg) to afford yellow-powdered (5,5)-La-NMe-linked-BINOL complex (254.0 mg, 0.30 mmol). 

Shibasaki made several improvements in the asymmetric Michael addition reaction using the previously developed BINOL-based (R)-ALB, (R)-6, and (R)-LPB, (R)-7 [1]. The former is prepared from (R)-BINOL, diisobutylaluminum hydride, and butyllithium, while the latter is from (R)-BINOL, La(Oz -Pr)3, and potassium f-butoxide. Only 0.1 mol % of (R)-6 and 0.09 mol % of potassium f-butoxide were needed to catalyze the addition of dimethyl malonate to 2-cy-clohexenone on a kilogram scale in >99% ee, when 4-A molecular sieves were added [15,16]. (R)-6 in the presence of sodium f-butoxide catalyzes the asymmetric 1,4-addition of the Horner-Wadsworth-Emmons reagent [17]. (R)-7 catalyzes the addition of nitromethane to chalcone [18]. Feringa prepared another aluminum complex from BINOL and lithium aluminum hydride and used this in the addition of nitroacetate to methyl vinyl ketone [19]. Later, Shibasaki developed a linked lanthanum reagent (R,R)-8 for the same asymmetric addition, in which two BINOLs were connected at the 3-positions with a 2-oxapropylene... 

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