Three-component spiropyran synthesis via tandem alkylation-condensation

One-pot, three-component Fischer indolisation–N-alkylation for rapid synthesis of 1,2,3-trisubstituted indoles

“…gave 3-isopropyl-1,2-dimethylindole 4i (121 mg, 95%) as an amorphous brown solid, spectroscopically identical to that previously reported. 4 3-Benzyl-1,2-dimethylindole, 4j. By the same general method, 4-phenylbutan-2-one (107 µL, 0.716 mmol, 1.05 eq.…”

“…1,2 Furthermore, they are versatile building blocks in synthesis, providing access to diverse heterocycles (e.g. tryptolines, 3 spiropyrans, 4 indolines, 5 oxindoles 6 and spirocycles 7 ), substrates for asymmetric dearomatisation, 8,9 and polymers and composite materials with energy storage and biomedical applications. [10][11][12] Accordingly, indole synthesis has a long and distinguished history, and the many published protocols for generating and elaborating the indole core ensure that few indole structures are beyond the reach of the present-day synthetic chemist.…”

“…[10][11][12] Accordingly, indole synthesis has a long and distinguished history, and the many published protocols for generating and elaborating the indole core ensure that few indole structures are beyond the reach of the present-day synthetic chemist. [13][14][15][16][17] Our recent studies into structurally-diverse spiropyrans 4,18 required a broad range of 1,2,3-trisubstituted indole building blocks and, to meet this demand, we have developed a rapid, cheap and concise one-pot, three-component sequence for their synthesis, based upon Fischer indolisation-N-alkylation, and the evolution of this process is described herein. 19 One-pot, multistep regimens can provide efficiency in terms of time, cost, yield, labour, energy and consumables, [20][21][22] and the combination of Fischer indole synthesis and indole N-alkylation is inherently geared towards successful application as a rapid one-pot process for two principal reasons: (i) Fischer indolisation and indole N-alkylation are robust, clean, high-yielding processes which generate minimal quantities of by-products or leftovers, hence are ideal within one-pot, multicomponent reaction cascades; (ii) indole N-alkylation is rapid (commonly < 1 hour) and whilst Fischer indolisation displays more varied reaction rate, use of microwave irradiation often leads to short reaction times (<10 minutes).…”

Three Complementary One‐Pot Four‐Component Reaction Sequences for Rapid, General and Direct Spiropyran Synthesis

“…Our recent research has pursued an overarching ideal that almost any spiropyran structure should be accessible from cheap, widely‐available feedstocks, using simple, robust and environmentally benign protocols [10,11] . Furthermore, spiropyran research is surprisingly narrow in its exploration of structural diversity, hence we have sought to develop synthetic pathways that allow straightforward diversification and that are amenable to combinatorial synthesis [11] .…”

Multistimuli-responsive fluorescent probes based on spiropyrans for the visualization of lysosomal autophagy and anticounterfeiting

“…[36][37][38] The drastically different properties between the two isomers, including their polarity, fluorescence properties, absorption properties and protonation capabilities, allow spiropyrans to exhibit distinct differences with azobenzene and fulgides. 39,40 Therefore, observing the relationship between the physicochemical properties of spiropyran derivatives and their structures is of vital interest for the development of novel molecular switch-type fluorescent probes and anticounterfeiting materials.…”