Organocatalytic Asymmetric Mannich Reaction of α‐Alkynylated Cyclohexanones and Dione Counterparts With C ‐Alkynyl N ‐Boc N
Manikanta Swami Pothana, Yi‐Hung Liu, Su‐Ying Chien, Bor‐Cherng HongABSTRACT
An enantioselective Mannich reaction of vinylogous carbonyl compounds with C ‐alkynyl N ‐Boc N , O ‐acetals has been developed. In the presence of a chiral phosphoric acid, β‐aminocarbonyl products are obtained in good yields and up to 96% ee across a range of substrates. Use of a cyclohexanedione nucleophile leads to a marked rate enhancement, but lower enantioselectivity, which can be additionally improved with cinchona‐derived hydrogen‐bonding catalysts at elevated temperature. The products 6a , 6j , and 6 g were further transformed into the 5/5/6 tricyclic frameworks via a Pauson–Khand reaction, highlighting their synthetic utility.