Access to Both Anomers of Pectenotoxin Spiroketals by Kinetic Spiroketalization

[structure: see text] A concise synthesis of both AB ring spiroisomers of the pectenotoxins is described. The nonanomeric AB spiroketal ring system of the pectenotoxins-1, -2, -3, and -6 is formed under very mild, kinetic spiroketalization conditions, along with the anomeric isomer. Only catalytic asymmetric transformations were used as the source of chirality in the synthesis route.