RESUMEN
[reaction: see text] The first syntheses of the pyridazinoindazolium alkaloids nigellicine and nigeglanine hydrobromide via a common intermediate are described. Ortho-lithiation/acylation and the direct amination of an isatin ring system are the key steps in the synthesis.
Asunto(s)
Alcaloides/síntesis química , Compuestos Heterocíclicos con 3 Anillos/síntesis química , Indazoles/síntesis química , Estructura Molecular , Nigella/químicaRESUMEN
[reaction: see text] Regioselective monoacylation of a diamine is achieved by including a suitably positioned 4-(dimethylamino)pyridine (DMAP) group within the molecule.
Asunto(s)
Diaminas/química , Piridinas/química , Acilación , Modelos Moleculares , Electricidad EstáticaRESUMEN
Tertiary allylic thionitrites undergo thermal rearrangement to alpha,beta-episulfide nitroso dimers via ring closure of allylthiyl radicals.
RESUMEN
Building on prototype 1, which achieves 120 degrees of phosgene-powered unidirectional rotation to rotamer 6 (see Figure 5 in the full article), 7 was designed to accomplish repeated unidirectional rotation (see Scheme 7). Compound 7 contains an amino group on each blade of the triptycene and a 4-(dimethylamino)pyridine (DMAP) unit to selectively deliver phosgene (or its equivalent) to the amine in the "firing position". The synthesis of 7 is described: the key constructive steps are a benzyne addition to an anthracene to generate the triptycene, a stilbene photocyclization to construct the helicene, and a Stille coupling to incorporate the DMAP unit. The DMAP unit was shown to regioselectively relay 1,1'-carbonyldiimidazole (but not phosgene) to the proximal amino group, as designed, but rotation of the triptycene does not occur. Extensive attempts to troubleshoot the problem led to the conclusion that the requisite intramolecular urethane formation, as demonstrated in the prototype (1 --> 4), does not occur with 7 (to give 85) or 97 (to give 100). We speculate that either (i) hydrogen bonding between the hydroxypropyl group and functionality present in 7 but absent from 1 or (ii) a Bürgi-Dunitz (or similar) interaction involving the DMAP (see 106) prevents achievement of a conformation conducive to intramolecular urethane formation.