Asymmetric double ring-opening of a C2h-symmetric bis-epoxide: improved enantiomeric excess of the product through enantioselective desymmetrisation and ‘proof-reading’ steps
作者:Alan Ironmonger、Peter Stockley、Adam Nelson
DOI:10.1039/b504972e
日期:——
A new strategy in asymmetric synthesis is described in which the desymmetrisation of a C(2h)-symmetric molecule is followed by a subsequent enantioselective 'proof-reading' step. The double asymmetric ring-opening of the bis-epoxide (1R*,3R*,5S*,7S*)-4,8-dioxa-tricyclo[5.1.0.0(3,5)]octane with azidotrimethylsilane, catalysed by a chiral chromium Salen catalyst, was studied. The reaction involves the
描述了一种不对称合成的新策略,其中,对C(2h)对称分子进行去对称,随后进行对映选择性“校对”步骤。手性催化剂催化双环氧化物(1R *,3R *,5S *,7S *)-4,8-二氧杂三环[5.1.0.0(3,5)]辛烷与叠氮三甲基硅烷的双不对称开环研究了铬萨伦催化剂。该反应涉及双环氧化物的初始不对称开环,得到中等对映体过量(约50%ee)的中间体。第二个开环步骤以72%的收率和70%的ee生成所需的二叠氮基二醇(1S,3S,4S,6S)-4,6-二叠氮基环己烷-1,3-二醇。校对的起源是由于中间体的次要对映异构体转移到了中心对称副产物上,一种改善所需产物对映体过量的方法。使用替代条件,对反应进行了优化,以产生> 98%ee的所需产物。