Stereoselective Synthesis of Quaternary Benzylic Carbons Using C2 Symmetric Imidazolines and Tetrahydrofuran as Electrophile

Alkylative ring opening of tetrahydrofuran in the presence of 9-BBN triflate is studied. Dianions derived from C 2 symmetric imidazolines induce excellent to modest acyclic diastereoselectivity to form quaternary benzylic centers, using the 9-BBN triflate/THF system or methyl iodide as electrophiles. The direction of the stereoinduction is consistent in both cases. Absolute configuration for the newly created stereogenic center was established by chemical correlation. Low-temperature NMR studies of the dilithiated intermediates 42 and 43 suggest the presence of N - and C -metalated compounds, where the metal-bearing benzylic carbon is sp 3 hybridized.