A synthetic sequence for the preparation of fully conjugated 2,7-disubstituted fluorazone (9H-pyrrolo[1,2--a]indol-9-one) derivatives has been developed comprising an Elming–Clauson–Kaas-type pyrrole formation, POCl3-mediated ring closure, selective halogenation and elongation of the conjugated backbone through cross-coupling reactions. As a proof of principle, this methodology was used to prepare for the first time two organic D–π–A dyes containing the fluorazone moiety. The new compounds display broad absorption bands in the visible-light region when adsorbed on nanocrystalline TiO2 and electrochemical properties compatible with their employment as photosensitizers in dye-sensitized solar cells. Small-scale photovoltaic devices fabricated with the fluorazone dyes yielded power conversion efficiencies in the range of 2.1–2.4 %, which correspond to approximately 70 % of the efficiency obtained with the reference organic dye DF15 under the same conditions

A manufacturing synthesis of 5-chlorophthalide has been elaborated. The key step of the procedure is ortho-lithiation of 4-chloro-N,N-diisopropylbenzamide, followed by formylation with dimethyl formamide. Reduction of the formyl moiety and subsequent ring closure, which can be carried out also in one pot, led to 5-chlorophthalide in high overall yield. The procedure has also been successfully adapted for the synthesis of the 5-fluoro and 5-trifluoromethyl analogues. The compounds thus obtained are useful building blocks in the synthesis of various heterocyclic ring systems.

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