• 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 and Jérôme Lacour
    Synthesis, 48 (19) , 2016, p3254-3262
    Keywords: azepine; azocine; carbenes; configurational stability; [1,2]-Stevens rearrangement; ylides
    DOI:10.1055/s-0035-1562467 | unige:86678 | Abstract | Article HTML | Article PDF | Supporting Info
 
Doubly bridged biphenyl azocines can be prepared in a single step through 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 eight-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–1). Interestingly, reactions performed at 40 °C retain a certain level of enantiospecificity (82–86%), avoiding, for the most part, thermal racemization of the starting material.

Other publications by these authors :
Besnard, Céline Brun, Elodie Bürgi, Thomas Grass, Stéphane Harthong, Steven 
Lacour, Jérôme 
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