Studies on the synthesis of pectenotoxin II: synthesis of a C(11)-C(26) fragment precursor via [3 + 2]-annulation reactions of chiral allylsilanes

see reaction]. A synthesis of tetracycle 2 corresponding to the C(11)-C(26) fragment of pectenotoxin II is described. The synthesis features two highly stereoselective 3 + 2]-annulation reactions of chiral allylsilanes, generated via allylboration of aldehydes with the chiral gamma-silylallylborane 4 or the gamma-silylallylboronate 19, for construction of the highly substituted C and E rings.