Synlett 2017; 28(16): 2179-2183
DOI: 10.1055/s-0036-1590816
letter
© Georg Thieme Verlag Stuttgart · New York

Superacid-Mediated Intramolecular Cyclization/Condensation: Facile One-Pot Synthesis of Spirotetracyclic Indanones and ­Indenes

Bokka Venkat Ramulu
Indian Institute of Technology Hyderabad, Kandi-502 285, Sangareddy District, Telangana, India   Email: gvsatya@iith.ac.in
,
Devarapalli Ravi Kumar
Indian Institute of Technology Hyderabad, Kandi-502 285, Sangareddy District, Telangana, India   Email: gvsatya@iith.ac.in
,
Gedu Satyanarayana*
Indian Institute of Technology Hyderabad, Kandi-502 285, Sangareddy District, Telangana, India   Email: gvsatya@iith.ac.in
› Author Affiliations
We are grateful to the Council of Scientific and Industrial Research (CSIR), New Delhi, for financial support [No. 02(0262)/16/EMR-II].
Further Information

Publication History

Received: 03 May 2017

Accepted after revision: 05 June 2017

Publication Date:
11 July 2017 (online)


Abstract

A facile, superacid-promoted, domino, one-pot synthesis of novel spirotetracyclic indanones through intramolecular Friedel–Crafts acylation/alkylation of α,β-unsaturated cinnamic acid esters is presented. Interestingly, when the β-aryl group contained electron-withdrawing substituents such as fluoro, chloro, or bromo, the reaction took a different mechanistic path and afforded arylindenes as the end products.

Supporting Information

 
  • References and Notes

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  • 22 Spirotetracyclic indanones 9; General Procedure An oven-dried Schlenk tube was charged with the appropriate β-aryl α,β-unsaturated ester 3ai (0.25 mmol) and DCE (2 mL) under N2. TfOH (0.1 mL, 1.5 mmol) was then added and the mixture was stirred at 50 °C for 30–36 h until the reaction was complete (TLC). The reaction was quenched with aq. NaHCO3, and the mixture was extracted with CH2Cl2 (3 × 20 mL). The organic layers were combined, washed with sat. brine, dried (Na2SO4), filtered, and concentrated under reduced pressure. The residue was purified by column chromatography (silica gel, PE–EtOAc) to give the appropriate spirotetracyclic indanone 9ai (76–90%). 6′-Methyl-2′,3′-dihydro-1,1′-spirobi[inden]-3(2H)-one (9b) Brown viscous liquid; yield: 54 mg (87%); TLC: Rf (3b) = 0.50, (9b) = 0.60 (PE–EtOAc, 96:4, UV detection). IR (MIR-ATR): 2922, 2851, 1710, 1601, 1461, 1287, 1236, 816, 763 cm–1. 1H NMR (400 MHz, CDCl3): δ = 7.79 (d, J = 7.8 Hz, 1 H, ArH), 7.57 (ddd, J = 7.3, 7.3, and 1.0 Hz, 1 H, ArH), 7.41 (ddd, J = 7.3, 7.3, and 1.0 Hz, 1 H, ArH), 7.27 (d, J = 7.8 Hz, 1 H, ArH), 7.21 (d, J = 7.8 Hz, 1 H, ArH), 7.08 (d, J = 7.8 Hz, 1 H, ArH), 6.57 (s, 1 H, ArH), 3.19–3.00 (m, 2 H, CH2), 2.94 (d, J = 18.6 Hz, 1 H, CH aHb), 2.87 (d, J = 18.6 Hz, 1 H, CHa H b), 2.55–2.44 (m, 1 H, CH2), 2.40–2.30 (m, 1 H, CH2), 2.22 (s, 3 H, ArCH3). 13C NMR (100 MHz, CDCl3): δ = 205.9 (s, C=O), 161.6 (s, ArC), 149.0 (s, ArC), 140.2 (s, ArC), 136.9 (d, ArC), 136.0 (s, ArC), 135.4 (d, ArCH), 128.1 (d, ArCH), 127.8 (d, ArCH), 125.1 (d, ArCH), 124.3 (d, ArCH), 123.3 (d, ArCH), 123.0 (d, ArCH), 54.4 [s, C(CH2)2], 52.4 (t, CH2), 42.9 (t, CH2), 30.8 (t, CH2), 21.2 (q, ArCH3). HRMS (APCI+): m/z [M + H]+ calcd for C18H17O+: 249.1274; found: 249.1279.
  • 23 Indenes 10; General Procedure An oven-dried Schlenk tube was charged with the appropriate β-aryl α,β-unsaturated ester 3jo (0.25 mmol) and DCE (2 mL) under N2. TfOH (0.1 mL, 1.5 mmol) was then added and the mixture was stirred at 50 °C for 12 h until the reaction was complete (TLC). The reaction was quenched with aq. NaHCO3 and the mixture was extracted with CH2Cl2 (3 × 20 mL). The organic layers were combined, washed with sat. brine, dried (Na2SO4), filtered, and concentrated under reduced pressure. The residue was purified by column chromatography (silica gel, PE–EtOAc) to give the appropriate indene 10jo (68–78%). 3-(4-Chlorophenyl)-5-methyl-1H-indene (10n) Brown viscous liquid; yield: 47 mg (78%). TLC: Rf (3n) = 0.45, (10n) = 0.60 (PE–EtOAc, 97:3, UV detection). IR (MIR-ATR): 2920, 1726, 1613, 1487, 1393, 1288, 1093, 1014, 885, 803, 731 cm–1. 1H NMR (400 MHz, CDCl3): δ = 7.57 (dd, J = 8.3 and 2.0 Hz, 2 H, ArH), 7.47 (dd, J = 8.3 and 2.0 Hz, 3 H, ArH), 7.38 (s, 1 H, ArH), 7.14 (d, J = 8.3 Hz, 1 H, ArH), 6.58 (t, J = 2.0 Hz, 1 H, CH=C), 3.49 (d, J = 2.0 Hz, 2 H, CH2), 2.45 (s, 3 H, ArCH3). 13C NMR (100 MHz, CDCl3): δ = 144.0 (s, ArC), 143.7 (s, ArC), 141.7 (s, ArC), 135.8 (d, ArC), 134.6 (s, ArC), 133.3 (s, ArC), 131.7 (d, ArCH), 129.0 (d, 2 C, ArCH), 128.7 (d, 2 C, ArCH), 125.9 (d, ArCH), 123.9 (d, ArCH), 120.7 (d, CH=C), 37.8 (t, CH2), 21.6 (q, ArCH3). HRMS (APCI+): m/z [M + H]+ calcd for C16H14Cl+: 241.0779; found: 241.0787.