Enantioselective [2+2] cycloaddition of unactivated alkenes with α-acyloxyacroleins catalyzed by chiral organoammonium salts

We report the first example of an organocatalytic enantioselective [2 + 2] cycloaddition reaction of unactivated alkenes with alpha-acyloxyacroleins to give optically active 1-acyloxycyclobutanecarbaldehydes and subsequent ring expansion to give optically active 2-hydroxycyclopentanone derivatives. Organoammonium salt, H-L-Phe-L-Leu-N(CH2CH2)(2)-reduced triamine center dot 2.6HNTf(2), is a highly effective chiral catalyst for the above enantioselective [2 + 2] cycloaddition. Thus, we have developed a novel and useful formal enantioselective [2 + 3] cycloaddition through two steps.