Kamlesh Sharma* Pages 1 - 4 ( 4 )
The present mechanism of addition of nucleophiles to the π-acid complexed alkynes is studied successfully by the assessment of energy of intermediates and activation parameters.
To elucidate the origin of the stereoselectivity and predicting the reaction pathways, the geometry optimizations of reactants, products, intermediates and transition states, were calculated by using density functional theory (DFT) at the B3LYP / 6-31+G(d) method.
The reaction mechanism of hydration of alkynes in catalysed synthesis of bis-spiroketal by DFT calculations is explored. The pyranyl enol ether is formed regioselectively by the first ring closure. Further, bis-enol ether is formed by second 6-exo-dig addition. Then, dehydration, followed by dehydrative ring closure finally gives bis-spiroketal product.
It is concluded that one of the most feasible reaction pathways comprises pyranyl enol ether and bis-enol ether formation as intermediates. Final cyclization step of product formation is endothermic. In terms of stereochemistry trans-product is found energetically more stable than cis-product and hence support the electivity of the reaction.
Reaction mechanism, DFT, Regioselectivity, Stereoselectivity, Tricyclic bis-spiroketal
Department of Chemistry, Faculty of Physical Sciences, Shree Guru Gobind Singh Tricentenary University, Gurugram 122505, Haryana