Lithium 5-(2-diphenylphosphinoethyl)-1,2,3,4-tetramethylcyclopentadienide: Regioselectivity of alkylation of the tetramethylcyclopentadienide anion

Treatment of a mixture of isomeric (2-chloroethyl)-1,2,3,4-tetramethylcyclopentadienes with lithium diphenylphosphide leads to novel 4,5,6,7-tetramethylspiro[2,4]hepta-4,6-diene among the reaction products. The reaction of spiroheptadiene obtained with excess LiPPh2 at elevated temperature affords lithium 5-(2-diphenylphosphinoethyl)-1,2,3,4-tetramethylcyclopentadienide in almost quantitative yield. the regioselectivity of alkylation of the tetramethylcyclopentadienide anion is estimated from quantum-chemical calculations performedab initio for C5Mc4H−. The full charges on the ring carbon atoms are determined within the framework of Bader's theory of atomic fragments in molecules.