Catalytic Tandem Friedel–Crafts Alkylation/C4–C3 Ring-Contraction Reaction: An Efficient Route for the Synthesis of Indolyl Cyclopropanecarbaldehydes and Ketones

Abstract

A general strategy for the synthesis of indolyl cyclopropanecarbaldehydes and ketones via a Brønsted acid-catalyzed indole nucleophilic addition/ring-contraction reaction sequence has been exploited. The procedure leads to a wide panel of cyclopropyl carbonyl compounds in generally high yields with a broad substrate scope.

4′-(N-(Propan-1,2-dienyl)pyrrol-2-yl)-2,2′:6′,2″-terpyridine

“…Additionally, the structure of 1 was further confirmed by Supplementary Materials 13 C NMR, as well as by HR-MS. For instance, the 13 As pointed out in the above-mentioned literature, the formation of compound 1 is not so "unexpected". Nevertheless, no trace of alkyne 2 was noticed, while N-propargylation of pyrrole and indole derivatives under similar reaction conditions are described in the literature [20,21]. Therefore, the obtention of 1 as the sole product is "unexpected".…”

A Catalytic One-Pot Synthesis of Indolyl Cyclobutanones

“…We recently reported the preparation of indole cyclopropylcarbaldehydes 3 through a tandem acid-catalyzed addition/ring-contraction reaction of 2-hydroxycyclobutanone (1) and indole (2a) (Scheme 2, a). 15 Continuing our studies in this research field, 16 we dis-covered that functionalized aldehyde 3a furnished the corresponding indolylcyclobutanone derivative 4a on treatment with PTSA at 50 °C (Scheme 2, b).…”

Transition-Metal-Free Silylation of Unactivated C(sp2)H Bonds with tert-Butyl-Substituted Silyldiazenes

“…When full conversion of the substrate was reached, the solid (sublimed) 1,3,5trimethoxybenzene was added to the crude mixture, which was then concentrated by rotary evaporation and analyzed by 1 H NMR.…”

“…entry 1 in Table 1) were in all cases identifiable by the color of the reaction mixture that remained diazene-like (red to pink). Yield determined by 1 H NMR on the crude reaction mixture with 1,3,5-trimethoxybenzene as internal standard. NR: no reaction…”

“…Reaction conditions: fluorobenzene 24 (0.1 mmol), diazene 1b (x eq. ), tBuOK (10 mol%) and THF (0.7 mL) at RT for 1 h. a Ratios were determined by 19 F{ 1 H} NMR. Conversions were not determined because of the high volatility of fluorobenzene 24.…”