Spirodiepoxide strategy to the C ring of pectenotoxin 4: synthesis of the C1-C19 sector.

The synthesis of a C1-C19 precursor to pectenotoxin 4 is presented. The strategy employed the functionalized allene shown. Key features include: olefin metathesis of two simple fragments to prepare the left portion of the allene-precursor, diastereoselective propargylation of an epoxy aldehyde to form the right portion, use of the DMDO-stable m-fluorobenzyl ether, and an allene spirodiepoxidation/C-ring formation cascade.

Conversions by dimethyldioxirane of 1-alkylbenzotriazoles into their N-oxides and of 2-alkylbenzotriazoles into 2-alkyl-trans-4,5,6,7-diepoxy-4,5,6,7-tetrahydrobenzotriazoles.

Dimethyldioxirane converted 1-alkylbenzotriazoles 4 to the corresponding 3-alkylbenzotriazole 1-oxides 5 in good yields, but transformed 2-alkylbenzotriazoles 12 into 2-alkyl-trans-4,5,6,7-diepoxy-4,5,6,7-tetrahydrobenzotriazoles 13.