CHEMOSELECTIVITY-TUNABLE [5+2] CYCLOADDITIONS OF ALLENAMIDES AND OXIDOPYRYLIUMS

[5 + 2] Cycloadditions between allenamides and oxidopyryliums are described. A series of substituted cycloheptanones were synthesized by this method with moderate to good yields. Interestingly, the chemoselectivity of this reaction could be tuned by changing the electron-withdrawing groups on the allenamide nitrogen atom. When oxazolidinone chiral auxiliaries were introduced in the allenamide substrate, [5 + 2] cycloadducts could be obtained with high diastereoselectivities. This reaction provides a useful synthetic protocol for the construction of highly substituted seven-membered rings.