Samarium(II)-promoted radical spirocyclization onto an aromatic ring.
Samarium(II)-mediated spirocyclization onto an aromatic ring was achieved by the reaction of methyl 4-(4-oxoalkyl)benzoates with SmI(2) in the presence of i-PrOH and HMPA, yielding methyl 1-alkyl-1-hydroxyspiro[4.5]dec-6-ene-8-carboxylates in moderate to high yields. Utilizing this chemistry, spiro[3.5] and -[5.5] systems, and sterically congested spiro[4.5] systems, were easily synthesized. For the successful conversion, appropriate activation of the aromatic ring has proven to be extremely important: while an ester or amide functionality on the aromatic ring can promote the spirocyclization, a sulfonamide substituent causes ortho cyclization.