@Article{Synthesis_48_3254, author = {S. Harthong and E. Brun and S. Grass and C. Besnard and T. B{\"u}rgi and J. Lacour}, title = {{Configurationally Stable Doubly Bridged Biphenyl Azocines through Copper-Catalyzed Double Carbene Insertions into the Corresponding Azepines}}, journal= {Synthesis}, ISSN = {0039-7881}, volume= {48}, number= {19}, pages = {3254-3262}, url = {http://www.thieme-connect.de/DOI/DOI?10.1055/s-0035-1562467}, eprint= {http://www.unige.ch/sciences/chifi/publis/refs_pdf/ref01527.pdf}, doi= {10.1055/s-0035-1562467}, keywords= {azepine;azocine;carbenes;configurational stability;[1,2]-Stevens rearrangement;ylides}, abstract = {{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 ($\Delta$G $^{‡}$ > 41 kcal·mol$^{{\frac{ }{ }}1}$). Interestingly, reactions performed at 40 °C retain a certain level of enantiospecificity (82{\frac{ }{ }}86%), avoiding, for the most part, thermal racemization of the starting material.}}, year = {2016} }