19507-10-9Relevant academic research and scientific papers
Pd-catalyzed ring assembly by vinylation and intramolecular heck coupling: A versatile strategy towards functionalized azadibenzocyclooctynes
J?ger, Michael,G?rls, Helmar,Günther, Wolfgang,Schubert, Ulrich S.
, p. 2150 - 2157 (2013)
A new modular approach based on Pd-catalyzed C-C bond formation is presented for the assembly of a benzannulated azocine scaffold, the key intermediate in the synthesis of functionalized azadibenzocyclooctynes (aza-DIBOs). The intramolecular ring-closing Heck coupling was investigated by variation of the C-X bond. The reaction rate is limited by the initial oxidative addition step and the regiochemistry strongly depends on the auxiliary phosphine. Under optimized conditions, the 8-endo regioisomer was obtained in 71 % yield over two steps (with no protecting group chemistry) or in one pot, inclusive of C-N bond formation. The practical generation of the octyne triple bond of a prototypical N-benzoyl aza-DIBO, without the need for chromatographic purification, is also described. The structural features, including those of the ring-strained cyclic octyne, were elucidated by NMR spectroscopy and X-ray crystallographic analysis. The high reactivity of the N-benzoyl aza-DIBO synthesized is demonstrated in a strain-promoted azide-alkyne cycloaddition reaction with an alkyl azide (k=0.38 M-1 s-1). Copyright
