Synthesis of the C10-C25 Northern Moiety of 22,23-Dihydroavermectin B1b

All articles of this category The C10-C25 spiroacetal moiety of 22,23-dihydroavermectin B 1b aglycone has been prepared starting from a previously described optically active C15-C25 sulfone precursor. An asymmetric Hoppe's homoaldol reaction between the intermediate C13-C25 unsaturated aldehyde and enantiomerically enriched titanium ( E )-2-butenyl N , N -diisopropylcarbamate, obtained in the presence of (-)-sparteine and tetra(isopropoxy)titanium, generates an anti 12 S ,13 S C10-C25 vinyl carbamate which was transformed into the E -vinylstannane required for the coupling reaction with the C1-C9 part of avermectins.