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Wu et al. Chem Synth 2023;3:6 https://dx.doi.org/10.20517/cs.2022.42 Page 7 of 17

Figure 2. Substrate scope of Nazarov-type cyclization. Reaction conditions: 0.2 mmol scale; 10 mol% 4a; CHCl (1.0 mL); 30 ℃; 12 h; 1:
3
2 = 1.5:1. Isolated yields.

naphthol 2g with a C7-methoxyl group could furnish product 3ag in a high yield of 81%. Interestingly, 2-
naphthalenethiol 2j serving as an analogue of 2-naphthol 2a could be employed for the Nazarov-type
cyclization under the standard conditions, giving product 3aj in a moderate yield.

In addition, we performed a 1 mmol scale reaction of 3-alkynyl-2-indolylmethanol 1a with 2-naphthol 2a
under the optimal reaction conditions [Scheme 3A]. In this case, product 3aa was afforded in a high yield of
80%, which demonstrated that this Brønsted acid-catalyzed Nazarov-type cyclization could be scaled up and
should have potential applications. In order to gain some insights into the organocatalytic Nazarov-type
cyclization, we performed some control experiments [Scheme 3B]. First, N-methyl-protected 3-alkynyl-2-
indolylmethanol 1o was employed as a substrate to the reaction with 2-naphthol 2a under the standard
reaction conditions with no reaction observed, which indicated that the NH group of 3-alkynyl-2-
indolylmethanol 1 played an important role in controlling the reactivity. Second, O-methyl-protected