The stereoselectivity associated with the coaddition of a chiral and an achiral cycloalkenyl anion to a squarate ester has been examined. The selective formation of polycyclic ketones is observed in all cases, although dual protonation at both of the available enolate sites in their penultimate cyclooctatrienyl dianion precursors was sometimes noted. Proof that the stereoselection was the result of interconversion between a pair of helical octateraene intermediates, with resultant erosion of original stereogenicity, was established by isolation of diastereomeric monoadducts and separate submission of these hydroxy cyclobutenones to the original reaction conditions. The final stages of the cascade proceed via the lower energy transition state option where nonbonded steric effects are skirted as much as possible. These features are coordinated with subsequent stereocontrolled trans/annular aldol reactions during the quenching process. The adherence to these mechanistic guidelines is so all-encompassing that product sterochemistry can be reliably predicted from the outset.