Reactions of 5,6-Dilithioacenaphthene-N,N,N′,N′-Tetramethyl-1,2-ethanediamine Complex with α-Diketones. I. cis-Directing 1:1 Cyclic Additions with Acyclic and Cyclic α-Diketones and Related Compounds

The title complex (3) is readily generated from 5,6-dibromoacenaphthene with butyllithium and the diamine in ether at −10–0 °C. The reaction of 3 with biacetyl gave cis-1,2,5,6-tetrahydro-1,2-dimethylcyclopent[fg]acenaphthylene-1,2-diol but no trans-isomer, whereas the reaction of pyracenequinone (PYQ) with methylmagne-sium bromide gave both the cis- and trans-dioh. The reactions of 3 with acenaphthenequinone and PYQ also gave cis-diols. On treatment with phenylboronic acid, these cis-diols quantitatively yielded the corresponding cyclic esters. The diols and their derivatives tend to form crystalline molecular compounds with solvent molecules. The stereoselectivity of the cyclic addition between 3 and the acyclic α-diketone can be best explained in terms of five-membered chelate-ring formation in a transition state.