Controlled Synthesis of α‐Allenic Ester and Spiro Ketone Derivatives from Tailored α‐Substituted Cycloalkanones Through Cascade Reactions: Exploring the Possible Reaction Pathways by Means of Semiempirical MO Calculations

Functionalized bicyclic electrophilic allenes and (or) spiro ketones have been obtained through a cascade reaction when acetylenic ω‐keto esters were treated with tetra‐n‐butylammonium fluoride (TBAF). The isolated products can be modulated by using different starting materials (i.e. varying ring size, spacer length) and reaction times. The results indicate that these reactions take place under kinetic control. In line with this, a semiempirical study was carried out in order to determine the preferred reaction pathways and the preferred cis/trans conformation of the bicyclic allenic derivatives. An excellent correlation was found between theoretical and experimental results, and the whole process dramatically depends on the presence of the HF molecule. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)