- Configurationally Stable Doubly Bridged Biphenyl Azocines through Copper-Catalyzed Double Carbene Insertions into the Corresponding Azepines
Steven Harthong, Elodie Brun, Stéphane Grass, Céline Besnard, Thomas Bürgi, Jérôme Lacour
Synthesis 2016, 48, 3254-3262
[ In memory of Jean-François Normant ]
Doubly-bridged biphenyl azocines can be prepared in a single step via copper-catalyzed reactions of a doubly-bridged biphenyl azepine and diazodiester reagents. Double [1,2]-Stevens rearrangements occur at 100 °C to afford doubly-tethered 8-membered rings (49 to 61%) as trans and cis regioisomers (1:1 ratio). These products present an axial chirality. ECD and VCD analyses of the separated enantiomers (CSP-HPLC) were used to assign the absolute configuration. High configurational stability is observed for both regioisomers as racemization does not occur after 1 week of heating at 208 °C in dodecane (ΔG‡ > 41 kcal/mol). Interestingly, reactions performed at 40 °C retain a certain level of enantiospecificity (82-86%) avoiding for the most part the thermal racemization of the starting material.
open archive unige:86678