Base‐Induced Sequential Cyclization–Rearrangement of Enantioenriched 3‐Aminoalkanoates to Five‐ and Seven‐Membered Lactams

By treatment with t BuLi, linear 3‐aminoalkanoates ( 4 ) were converted stereoselectively into five‐ and seven‐membered lactams ( trans‐ 5 and cis‐ 6 ). Initial cyclization to azetidin‐2‐one with subsequent aza‐[1,2] and [2,3] rearrangement is the probable mechanistic pathway from 4 to 5 and 6 . Although enantioenriched 4 was converted into nearly racemic 5 and 6 , a linear 3‐amino‐2‐methylalkanoate ( 17 ) with 90 %  ee bearing chirality at the ester α‐position afforded an all‐ cis seven‐membered lactam ( 18 ) bearing three asymmetric centers with 85 %  ee .