Translation of Pseudo-Cross-Conjugation into Chemistry: Cycloadditions of Mesomeric Betaines to the New Ring System Spiro[indazole-3,3‘-pyrrole]
作者:Andreas Schmidt、Tobias Habeck、Anika Sabine Lindner、Bohdan Snovydovych、Jan Christoph Namyslo、Arnold Adam、Mimoza Gjikaj
DOI:10.1021/jo062391r
日期:2007.3.1
Indazolium-3-amidates (X-ray analysis), readily available on trapping the N-heterocyclic carbene indazol-3-ylidene with isocyanates, underwent [3 + 2]-cycloadditions with activated triple bonds to spiro[indazole-3,3'-pyrroles]. A combination of NMR techniques such as heteronuclear single quantum coherence (HSQC), heteronuclear multiple bond correlation (HMBC), nuclear Overhauser enhancement spectroscopy (NOESY), and H-1/N-15 correlations were applied to elucidate the structures of the cycloadducts.
Pseudo-Cross-Conjugated Mesomeric Betaines and <i>N</i>-Heterocyclic Carbenes of Indazole
betaines (PCCMB) and derivatives of the indazole alkaloid Nigellicin. They decarboxylate on heating to give intermediary N-heterocyclic carbenes of indazole that can be trapped with iso(thio)cyanates to amidates. Alternatively, 1.2-dimethylindazolium-3-amidates can be prepared starting from the corresponding 1H-indazol-3-carboxylic acid which is converted into its chloride, reacted with anilines and deprotonated