BINOL allyltributylstannane

A 25 x 17-cm silica gel (Davisel 633) column is used. Initially, hexanes are used as eluant to elute recovered allyltributylstannane, then 9 1 hexane acetone is used as eluant to isolate the product. Further elution of the column with 8 2 hexane acetone gives 0.9 g (80%) of crude recovered BINOL which can be further purified by chromatography over silica gel to give 0.8 g (70%) of pure BINOL. 

A chiral BINOL-indium(in) complex has been used to catalyse the addition of allyltributylstannane to aldehydes in high ee.184... 

The enantioselective addition of allyltributylstannanes to aldehydes and ketones has been performed in the presence of various chiral indium(III) complexes derived from (R)-BINOL,136 (S )-BINOL,137,138 and PYBOX.139,140... 

Fhal and Renaud have examined the alkylation of a radical generated from the a-iodoimide 333 with a variety of Lewis acids, as shown in Sch. 42 [70]. The stereogenic step in this process would be hydrogen atom transfer from tin to a Lewis acid-com-plexed radical generated from 333. Initial screening was performed for the reaction of allyltributylstannane and imide 333, which was conducted by precomplexation of the imide with the Lewis acid and then addition of the stannane in the presence of AIBN under irradiation at 10 °C. The Lewis acid prepared from BINOL was ineffective whereas that prepared from the bis-sulfonamide 337 was slightly superior to that from the TADDOL ligand 339. 

The reaction of methallyltri-n-butylstannane 117 with achiral aldehydes is also effectively promoted by the binol-Ti complex [89 c]. In all but one case (cyclo-hexanecarboxaldehyde), the yields and enantioselectivities observed with the methallylstannane are identical or higher than those obtained in the reactions with allyltributylstannane with only 10 mol% of the binol-Ti complex (Scheme 10-50). Insight into the nature of the titanium catalyst is provided by the observation of asymmetric amplification [89 b] and chiral poisoning [89 g]. An intruiging hypothesis on the origin of enantioselection in allylation and related reactions [89 h]. 

During the past two decades the homogeneous and heterogeneous catalytic enan-hoselective addition of organozinc compounds to aldehydes has attracted much attention because of its potential in the preparation of optically active secondary alcohols [69]. Chiral amino alcohols (such as prolinol) and titanium complexes of chiral diols (such as TADDOL and BINOL) have proved to be very effective chiral catalysts for such reactions. The important early examples included Bolm s flexible chiral pyridyl alcohol-cored dendrimers [70], Seebach s chiral TADDOL-cored Frechet-type dendrimers [28], Yoshida s BINOL-cored Frechet-type dendrimers [71] and Pu s structurally rigid and optically active BlNOL-functionalized dendrimers [72]. All of these dendrimers were used successfully in the asymmetric addition of diethylzinc (or allyltributylstannane) to aldehydes. 

Functionalized allyltributylstannanes can also be used in the BINOL/Ti-cata-lyzed reaction and addition of P-substituted allyl groups with heteroatoms in the side chain to aldehydes has been achieved with a high degree of enantiocon-trol [ 16]. The catalytic asymmetric allylation has been successfully applied to to -tal syntheses of the macrohdes (l )-(-i-)-ricinelaidic acid lactone and (-)-gloe-osporone [21]. 

An effective chiral catalyst for asymmetric allylation of aldehydes or ketones is the complex formed between the axially chiral l,l -bi-2-naphthol (BINOL) 164 and a titanium(IV) salt." Addition of allyltributylstannane to an aldehyde using this Lewis acid gives the product homoallylic alcohol with high optical purity. For example, allylation of iso-butyraldehyde gave the alcohol 165 as a 98 2 ratio of enantiomers (1.155). Use of (5)-BINOL gave the other enantiomer of the product. 

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