Reactions of (Vinylimino)phosphoranes and Related Compounds: Access to the Azacarbolines and Aplysinopsines

Dipyrido[1,2-a;3′,4′-d]imidazole systems

“…5,7 Adaptation of our general heterocyclic synthesis strategy to the synthesis of relatively unknown heterocyclic systems with unexplored biological activity was our next goal. Synthetic procedures for the construction of dipyridoimidazole motifs are very rare 10 and recent publications describe syntheses involving reaction of 2-aminopyridine derivatives with an appropriate dihalogenated pyridine system catalysed by palladium acetate or palladium acetate/copper (I) iodide in Buchwald-Hartwig type processes. 11,12 Alternatively, annelation of imidazo[1,2-a]pyridine systems has allowed the synthesis of some functionalised systems, albeit in low yield.…”

“…11,12 Alternatively, annelation of imidazo[1,2-a]pyridine systems has allowed the synthesis of some functionalised systems, albeit in low yield. 10,13,14 In all cases, further functionalisation of the heterocyclic core scaffolds to provide analogue systems has not been reported because, in part, the multi-step synthesis of functionalised dibrominated pyridine starting materials can be very difficult indeed.…”

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“…This has been cyclized by treatment with nitrogen nucleophiles, such as ammonia, aliphatic amines, and hydrazines to give aplysinopsin derivatives [13]. In this context, a highly effective method for the synthesis of aza-carboline and aza-aplysinopsin mimic structures from heterocumulenes [14] and from alumina-supported heterocumulenes [15] have also been reported.…”

The Synthesis Aplysinopsins, Meridianines, and Related Compounds

“…In this context, the aplysinopsin skeleton has been prepared from iminophosphoranes 14, obtained from 3-formylindole derivative 13 in two steps, followed by the reaction with methyl isocyanate to form the corresponding carbodiimide 15. Using the same synthetic approach, some highly effective methods for the synthesis of azaaplysinopsin mimic structures 19 from aldehydes 17 via the heterocumulenes 18 [23,24] have been reported. Deprotection by treatment with formic acid at reflux furnished aplysinopsin derivatives 8 [22].…”