Stereoselective acylation of the E,E-vinylketene silyl N,O-acetal possessing a chiral auxiliary has been achieved by using acid anhydrides and SnCl4. Acid anhydrides having alkyl chains gave the adducts in excellent stereoselectivity. The formal synthesis of khafrefungin has been accomplished by the methodology.
[structure: see text] A convergent total synthesis of khafrefungin was accomplished on the basis of (1) the highly stereoselectiveTiCl4-mediated vinylogous Mukaiyama aldolreaction using vinylketene silyl N,O-acetal and (2) syn-selective aldolreaction of enal 5a and ethyl ketone 6 followed by anti-dehydration under Mitsunobu conditions.