Gold Catalysis: Switching the Pathway of the Furan-Yne Cyclization
作者:A. Stephen K. Hashmi、Matthias Rudolph、Jürgen Huck、Wolfgang Frey、Jan W. Bats、Melissa Hamzić
DOI:10.1002/anie.200900887
日期:2009.7.27
Changing tracks: By the use of alkynyl ethers as directing elements, the furan‐yne cyclization enters a new reaction pathway. Instead of phenols, tetracycles containingtwoheteroatoms and two new stereocenters are formed (see scheme).
The First Example of Saccharin-Lithium Bromide Catalysis: Direct Synthesis of N-Tosylimines from Alcohols
作者:Rajesh Patel、Vishnu P. Srivastava、Lal Dhar S. Yadav
DOI:10.1002/adsc.201000193
日期:——
The first procedure to access N‐tosylimines directly fromalcohols under mild and neutral conditions is reported. The protocol involves saccharin‐lithium bromide‐catalyzed oxidation of alcohols to aldehydes/ketones with chloramine‐T followed by their condensation with the in situ generated oxidation by‐product p‐toluenesulfonamide in the same reaction vessel to afford N‐tosylimines in 40–90% overall
Highly Stereoselective Ylide Aziridination of <i>N</i>-Sulfonylimines with Sulfonium Propargylides: A Simple Way To Synthesize Scalemic Acetylenylaziridines
Under phase-transfer or low-temperature conditions, the ylide generated from diphenylsulfonium salt 2 readily reacts with N-sulfonylimines 1 to give acetylenylaziridines in excellent yields, but low to moderate cis/trans selectivity. When using n-BuLi as the base to generate the ylide at low termperature, product 3 with an intact silyl protecting group is obtained. t-BuOK, however, leads to desilylation product 4. With Cs2CO3 as the base, dimethylsulfonium salts 6, 21, and 22 show much better cis/trans selectivity (>98:2) than diphenylsulfonium salt 2. The asymmetric version of the above aziridination reaction using camphor-derived sulfonium salts 12-14 and 20 gives chiral aziridines with ee values up to 85%. Both (2R,3S)-(-)-3 and (2S,3R)-(+)-3 can be prepared from 12/20 or 13/14, respectively. Ylides produced from telluronium salt 7 failed to react with imine la at room temperature, but the reaction succeeded at low temperature. Arsonium ylides from 8 cannot react with N-sulfonylimines under both sets of conditions.
Brown,C. et al., Journal of the Chemical Society. Perkin transactions II, 1978, p. 822 - 828
作者:Brown,C. et al.
DOI:——
日期:——
Asymmetric Aziridination over Ylides: Highly Stereoselective Synthesis of Acetylenyl-N-sulfonylaziridines
作者:An-Hu Li、Yong-Gui Zhou、Li-Xin Dai、Xue-Long Hou、Li-Jun Xia、Lin Lin