Studies Directed Toward the Synthesis of Acylated Phloroglucinols

The synthesis and application of α-allenyl ketones directed toward the synthesis of polycyclic polyprenylated acylphloroglucinols are described. A functionalized α-allenyl ketone was synthesized in twelve steps starting from 2-methyl-2-cyclohexenome in 24% overall yield. The α’ stereocenter in the α-allenyl ketone was stereoselectively quaternized using a Tsuji allylation, Mukaiyama adol condensation sequence to afford C-1 functionalized allenyl cyclohexanone building blocks. A survey of acetals and reaction conditions for the Mukaiyama reaction suggested that 3-tert-butyldiphenylsiloxypropanal dimethyl acetal could be used, and indeed this reagent in the presence of TiCl4∙Ti[OCH(CH3)2]4 gave the aldol product in 63% yield. The furthest advanced intermediate was prepared from 2-methyl-2-cyclohexenone in sixteen steps in 6% overall yield