Asymmetric Catalysis of Diels-Alder Cycloadditions by an MS-Free Binaphthol-Titanium Complex: Dramatic Effect of MS, Linear vs Positive Nonlinear Relationship, and Synthetic Applications
Asymmetric Diels-Alder (D.-A.) reaction of 5-hydroxynaphthoquinone (juglone) with butadienyl acetate catalyzed by the binaphthol-derived chiral titanium (BINOL-Ti) complex 1 proceeds in only 9% ee in the presence of molecular sieves (MS). Remarkably, however, this reaction proceeds in 76-96% ee with BINOL-Ti complex 1 freed from MS to provide the endo-adducts useful for the synthesis of anthracyclines and tetracyclines. The solid MS-free BINOL-Ti complex 1 is stable for months at -20 degrees C, Enhancements in endo selectivity and asymmetric induction are observed with the MS-free BINOL-Ti 1 also in the catalyzed D.-A. cycloaddition of methacrolein and glyoxylate with 1,3-dienol ethers and esters. The glyoxylate adducts can be converted to the mevinolin (compactin) intermediates. Surprisingly, the MS-free complex 1 exhibits not only a linear relationship between the ee's of BINOL-Ti 1 and the D.-A. products but also a positive nonlinear effect (asymmetric amplification), depending simply on the mixing manner of (R)-1 with (S)-1 or (+/-)-1.
Chiral titanium complex-catalyzed Diels-Alder reaction: A practical route to anthracycline intermediates
Asymmetric Diels-Alder reactions of methacrolein and 1,4-naphthoquinone with 1,3-dienol derivatives catalyzed by the chiral binaphthol (BINOL)-derived titanium complex 1 are shown to provide the corresponding endo-adducts in high enantiomeric purity. The naphthoquinone adduct can serve as a synthetic intermediate of tetracycline antibiotics.
The 1-aza-Cope rearrangement
作者:Pei Lin Wu、Min Chu、Frank W. Fowler
DOI:10.1021/jo00240a006
日期:1988.3
Diels-alder reactions: Rate acceleration promoted by a biphenylenediol
作者:T.Ross Kelly、Premji Meghani、Vadiraj S. Ekkundi
DOI:10.1016/s0040-4039(00)97402-1
日期:1990.1
The presence of biphenylenediol 8 accelerates the rate of some Diels-Alderreactions. Catalysis via a complex involving two hydrogen bonds (see 6) is proposed.