Ascididemine (9H‐quino[4,3,2‐de][1,10]phenanthrolin‐9‐one) (1) and an isomer (9H‐quino[4,3,2‐de][1,7]phenanthrolin‐9‐one) (4) have been synthesized starting from 1,4‐dimethoxyacridone (7). The acridone was converted into 1,4‐dimethoxy‐9‐ethynylacridine (11) by a triflate coupling. The ethynylacridine was converted in one‐pot into 3H‐6‐methoxypyrido[2,3,4‐kl]acridine (15) by reaction with sodium diformylamide; the mechanism of this key transformation is discussed. Conversion into 6H‐4‐bromopyrido[2,3,4‐kl]acridin‐6‐one (19) and 6H‐pyrido[2,3,4‐kl]acridin‐6‐one (17), followed by reaction of each of these under high pressure conditions with acrolein N,N‐dimethylhydrazone, gave ascididemine and its isomer, respectively.

Batzellines A and B (1a, b) and isobatzellines A and B (2a, b) are 1,3,4,5‐tetrahydropyrrolo[4,3,2‐de]quinoline‐containing marine alkaloids characterized by the presence of a methylthio substituent at C‐2 of the tricyclic system. We describe here the total synthesis of these natural compounds following the synthetic strategy that we have used previously for the synthesis of damirones A and B, batzelline C, isobatzelline C, discorhabdin C, and makaluvamines A, B, C, and D. The introduction of the methylthio group by electrophilic substitution of a pyrrolo[4,3,2‐de]quinoline, appropriately substituted and in a suitable oxidation state, is the key step in the success of these syntheses.

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