Synthesis of\nConsecutive All-Carbon Quaternary Centers\nvia Three-Step Reactions

Consecutive all-carbon quaternary\ncenters were synthesized in three\nsteps from the corresponding ketones. The three reactions were (1)\nKnoevenagel condensation of ketone and malononitrile to afford dicyanoalkene,\n(2) 1,4-addition reaction of a Grignard reagent to dicyanoalkene,\nand (3) oxidative transformation of a malononitrile moiety to an ester,\nthioester, amide, and α-nitroketone. This method was applied\nto the synthesis of 17α-methyl steroids with a good yield and\nexcellent diastereoselectivity. Moreover, three consecutive all-carbon\nquaternary centers were also synthesized.