LITHIUM OSPHINOETHYL)-1,2,3,4-TETRAMETHYLCYCLOPENTADIENIDE - REGIOSELECTIVITY OF ALKYLATION OF THE TETRAMETHYLCYCLOPENTADIENIDE ANION

Treatment of a mixture of isomeric 2-chloroethyl)-1,2,3,4-tetramethylc yclopentadienes 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 te mperature affords lithium osphinoethyl)-1,2,3,4-tetramethylcyclopentad ienide in almost quantitative yield. The regioselectivity of alkylatio n of the tetramethylcyclopentadienide anion is estimated from quantum- chemical calculations performed ab initio for C5Me4H-. The frill charg es on the ring carbon atoms are determined within the framework of Bad er's theory of atomic fragments in molecules.