Catalysts binaphtholate

A very high asymmetric induction was observed when the reaction between cyclopentadiene and methacrolein was performed using 0.5 mol% of binaphthol catalyst 326209. Diels-Alder adduct (2R)-322 was formed with up to 97.8% ee within 4 h at — 80 °C. 

Yamamoto and colleagues showed that very high enantioselectivities and yields were obtained in the cycloadditions of cyclopentadiene with several a-substituted acrylic aldehydes using binaphthol catalyst 387 (equation 116). 

Binaphthol catalyst 417 proved effective in the cycloadditions of 1-alkoxy-l,3-butadienes with methacrolein and 1,4-naphthoquinone257. More recently, it was found that the use of molecular sieves was essential for the in situ preparation of the catalyst, but also that this had dramatic effects on the enantioselectivity258. In the presence of molecular sieves, the cycloaddition of juglone (342) with 1-acetoxy-l,3-butadiene was catalyzed by 10 mol% of 417 to give cycloadduct 343 with only 9% ee. In the absence of molecular sieves, the enantiomeric excess increased to 76-96% (equation 124). 

An ytterbium binaphthol catalyst was successfully applied in the cycloaddition reactions of 3-carbomethoxy-2-pyrone (454) with O- and S-subsli luted olefins like 455 and 280d. Upon heating, the products lost carbon dioxide to yield chiral cyclohexadienes 456 (equation 136). S -substituted olefins generally gave higher ee values than the corresponding O-substituted ones. 

Methyl 2-methoxy-5,6-dihydro-2H-pyran-6-carboxylate (2 R = Me) can be obtained in optically active form by condensation of diene 1 with methyl glyoxylate in the presence of dichlorotitanium (R)-binaphthol catalyst (3) [45]. 

Shibasaki and co-workers disclosed a general asymmetric Strecker-type reaction that was controlled by bifunctional Lewis acid-Lewis base catalyst 14 [10], N-Fluorenylimines 15 underwent catalytic asymmetric Strecker-type reactions with binaphthol catalyst 14 to give a-aminonitriles 16 in good to excellent enantioselectivities and yields (Scheme 6). a-Aminonitrile 16 (R = Ph) could then be converted to a-aminoamide 17 in several steps. Aromatic, aliphatic, heterocyclic and a,/f-unsaturated imines 15 were used as general substrates in these reactions. The origin of the highly enantioselective cataylsis by 14 is believed to be attributed to the simultaneous activation of imines and trimethylsilyl cyanide by the... 

It should be noted that the new binaphthol catalyst 2-69 b may give better results in some cases, but not always. Thus, the cis-selectivity is decreased in the reaction of 2-65 and 2-66 with nearly identical enantioselectivity (Fig. 2-19). 

Further work with the molecular sieve-free Ti(IV)-binaphthol catalyst 56 showed that 1 -alkoxydienes react with methacrolein to afford cyclohexene products possessing a quaternary center adjacent to a stereo chemically defined secondary urethane in near diastereomeric purity and high enantiomeric excess (Scheme 44). 

Titanium complexes that are similar to Duthaler s ( 2.5.2) can be generated from TiCl4, Ti(Or-Pr)4 and diacetoneglucose 1.48. These complexes catalyze asymmetric hetero-Diels-Alder reactions, and give high enantiomeric excesses [827], Corey and coworkers [828] also prepared a chiral titanium catalyst derived from cis-/V-sulfonyl-2-amino-1 -indanol and used this to catalyze asymmetric Diels-Alder reactions. Buchwald and coworkers [829, 830] have proposed the use of titanocene-binaphthol catalysts for asymmetric hydrogenation of imines or trisubsti-tuted olefins. 

Nakajima also developed an enantioselective addition of lithium acet-ylides to ketones in the presence of chiral lithium binaphtholate catalyst 8 (Scheme 2.7). This is the first example of the catalytic enantioselective addition of lithium acelylides to carhonyl compounds without the aid of other metal sources, such as titanium(iv) and zinc(n) species. 

Scheme 24.16 Asymmetric aza-Morita-Baylis-Hillman reaction catalysed by bifunctional binaphthol catalysts.

---