An efficient, formal [4 + 2] synthesis of synthetically valuable piperidin-4-ones from secondary amines; in two steps has been achieved via a key gold catalysis without the purification of tertiary amine intermediates. This reaction is selective toward the less-substituted alkyl group and shows moderate to excellent diastereoselectivities. Its synthetic potential in alkaloid synthesis is demonstrated in a highly diastereoselective synthesis of (+/-)-cermizine C.