| Abstract
| - Catalytic asymmetric hetero Diels−Alder (HDA) reactions using a chiral zirconium complex havebeen developed. The reactions of aldehydes with Danishefsky's dienes proceeded smoothly to afford thecorresponding pyranone derivatives in high yields with high diastereo- and enantioselectivities in the presenceof a chiral zirconium complex, which was prepared from zirconium tert-butoxide, (R)-3,3‘-diiodobinaphtholor its derivative, a primary alcohol, and a small amount of water. It is noted that 2,3-trans-pyranone derivativeswere obtained with remarkably high diastereo- and enantioselectivities in the reaction with 4-methylDanishefsky's diene. This is the first example of catalytic asymmetric trans-selective hetero Diels−Alderreactions of aldehydes. Furthermore, asymmetric HDA reactions with 4-benzyloxy Danishefsky's dieneswere conducted to afford 2,3-cis-pyranone derivatives in high selectivities. Isolation of an intermediate ofthis asymmetric hetero Diels−Alder reaction indicated that the reaction proceeded in a stepwise cycloadditionpathway. Finally, these catalytic, asymmetric hetero Diels−Alder reactions were successfully applied toconcise syntheses of biologically important natural pyranone derivatives, (+)-Prelactone C and (+)-9-deoxygoniopypyrone.
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