Direct Synthesis of Highly Substituted 2-Cyclohexenones and Sterically Hindered Benzophenones Based on a [5C + 1C] Annulation

The regiospecific [5C + 1C] annulation of readily available α-alkenoyl ketene (S,S)-acetals 1 with aryl methyl ketones 2, the less active methylene compounds, has been developed. Upon treatment of 1 with 2 in the presence of t-BuOK in DMF at room temperature, highly substituted 2-cyclohexenones 3 were synthesized in high to excellent diastereoselectivities with high yields. On the basis of this strategy, sterically hindered benzophenones 4 were conveniently prepared via the iodonation−aromatization of 2-cyclohexenones 3 with I2 in MeONa/MeOH basic medium. Furthermore, benzophenones 4 were also obtained directly from 1 and 2 following a sequential [5 + 1] annulation−iodonation−aromatization procedure in a one-pot operation.