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General One‐Pot Reductive gem ‐Bis‐Alkylation of Tertiary Lactams/Amides: Rapid Construction of 1‐Azaspirocycles and Formal Total Synthesis of (±)‐Cephalotaxine
Author(s) -
Xiao KaiJiong,
Luo JieMin,
Xia XiaoEr,
Wang Yu,
Huang PeiQiang
Publication year - 2013
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201302096
Subject(s) - amide , chemistry , nucleophile , reagent , alkyl , alkylation , combinatorial chemistry , functional group , total synthesis , ring (chemistry) , electrophile , organic chemistry , catalysis , polymer
Amides are a class of highly stable and readily available compounds. The amide functional group constitutes a class of powerful directing/activating and protecting group for CC bond formation. Tertiary tert ‐alkylamine, including 1‐azaspirocycle is a key structural feature found in many bioactive natural products and pharmaceuticals. The transformation of amides into tert ‐alkylamines generally requires several steps. In this paper, we report the full details of the first general method for the direct transformation of tertiary lactams/amides into tert ‐alkylamines. The method is based on in situ activation of amide with triflic anhydride/2,6‐di‐ tert ‐butyl‐4‐methylpyridine (DTBMP), followed by successive addition of two organometallic reagents of the same or different kinds to form two CC bonds. Both alkyl and functionalized organometallic reagents and enolates can be used as the nucleophiles. The method displayed excellent 1,2‐ and good 1,3‐asymmetric induction. Construction of 1‐azaspirocycles from lactams required only two steps or even one‐step by direct spiroannelation of lactams. The power of the method was demonstrated by a concise formal total synthesis of racemic cephalotaxine.