Pt~(II)-Catalyzed Synthesis of 9-Oxabicyclo[3.3.1]nona-2,6-dienes from 2-Alkynyl-1-carbonylbenzenes and AUylsilanes by an Allylation/Annulation Cascade

摘要

AUylsilanes commonly undergo[3+2]or[~(2+)2]annulation reactions with aldehydes to give substituted tetrahydrofurans or oxetans,an approach that has been applied to the syntheses of natural products.New[3+2]and[4+2]annulations were reported for aldehyde substrates bearing an alpha-or beta-siloxy group,but these annulations required 1.0-5.0 equivalents of a Lewis acid(BF3·Et2O,TiCl4,or SnCl4).Our objective was to explore new annulations of allysilanes with functionalized aldehydes by using soft-acid-metal species in catalytic proportions.Herein,we report a one-pot Pt~(II)-catalyzed synthesis of 9-oxabicyclo[3.3.1]nona-2,6-dienes by a tandem allylation/annulation reaction of the oxo-alkyne functionalities with 2-substituted allylsilanes(see Table 1).The importance of this new synthesis is that it provides easy access to two classes of bioactive molecules,I-TV and V,which are comprised of the oxatricyclic framework that showed biological effects in the central nervous system,as well as HIV-1 inhibitory activities(Figure 1).