Metal-Free Intramolecular Carbonyl-Olefin Metathesis of ortho-Prenylaryl Ketones

Abstract

On treatment with boron trifluoride etherate as a Lewis acid, acetophenone and benzophenone derivatives bearing a prenyl (or a related) side chain in ortho-position were shown to undergo intramolecular carbonyl-olefin metathesis, in the absence of any transition-metal catalyst. The cationic cyclization process is supposed to proceed via an oxetane intermediate, which fragments to give the cyclization product (indene or 1,2-dihydronaphthalene) and a ketone (acetone) as a stoichiometric by-product. Several substrates were shown to afford the metathesis products with up to 93% yield.

olefin metathesis - cyclization - Lewis acids - carbenium ions - oxetanes - natural products

References and Notes

For selected reviews, see:

1a Ivin FJ. Olefin Metathesis   Academic Press; London: 1983. 

1b Schmalz H.-G. Angew. Chem. Int. Ed.  1995,  34:  1833 

1c Grubbs RH. Miller SJ. Fu GC. Acc. Chem. Res.  1995,  28:  446 

1d Grubbs RH. Chang S. Tetrahedron  1998,  54:  4413 

1e Schuster M. Blechert S. Angew. Chem. Int. Ed.  1997,  36:  2036 

1f Schrock RR. Tetrahedron  1999,  55:  8141 

1g Fürstner A. Angew. Chem. Int. Ed.  2000,  39:  3012 

1h Schrock RR. Hoveyda AH. Angew. Chem. Int. Ed.  2003,  42:  4592 

1i Deiters A. Martin SF. Chem. Rev.  2004,  104:  2199 

2a Trnka TM. Grubbs RH. Acc. Chem. Res.  2001,  34:  18 

2b Armstrong SK. J. Chem. Soc., Perkin Trans. 1  1998,  371 

2c Dragutan I. Dragutan V. Filip P. ARKIVOC  2005,  (x):  105 

2d Wengrovius HJ. Sancho J. Schrock RR. J. Am. Chem. Soc.  1981,  103:  3932 

2e Grubbs RH. Handbook of Metathesis   Wiley-VCH; Weinheim: . 

3a Astruc D. New J. Chem.  2005,  29:  42 

3b Basset J.-M. Leconte M. Chemtech  1980,  10:  762 

4a Herrison J.-L. Chauvin Y. Makromol. Chem.  1970,  141:  161 

4b Katz TJ. McGinnis J. J. Am. Chem. Soc.  1977,  99:  1903 

4c Leconte M. Basset JM. Quignard F. Larroche C. Mechanistic Aspects of the Olefin Metathesis Reaction, in Reactions of Coordinated Ligands   Vol. 1:  Braterman PS. Plenum; New York: 1986.  p.371 

5a Pine SH. Zahler R. Evans DA. Grubbs RH. J. Am. Chem. Soc.  1980,  102:  3270 

5b For a review, see: Grubbs RH. Pine SH. Comprehensive Organic Synthesis   Vol. 5:  Trost BM. Fleming I. Pergamon Press; Oxford: 1991.  p.1115 

6a Fu GC. Grubbs RH. J. Am. Chem. Soc.  1993,  115:  3800 

6b Nicolaou KC. Postema MHD. Claiborne CF. J. Am. Chem. Soc.  1996,  118:  1565 

6c Nicolaou KC. Postema MHD. Yue EW. Nadin A. J. Am. Chem. Soc.  1996,  118:  10335 

6d Majumder U. Rainier JD. Tetrahedron Lett.  2005,  46:  7209 

6e Iyer K. Rainier JD. J. Am. Chem. Soc.  2007,  129:  12604 

7 Slavov N. Cvengros J. Neudörfl J.-M. Schmalz H.-G. Angew. Chem. Int. Ed.  2010,  49:  7588 

8 Konieczny MT. Maciejewski G. Konieczny W. Synthesis  2005,  1575 

9

For a summary of data see: Cambridge Crystallographic Data Centre; Deposit Number: CCDC-836866.

10a Jackson AC. Goldman BE. Snider BB. J. Org. Chem.  1984,  49:  3988 

For Lewis acid induced carbonyl-alkyne metathesis reactions (related to enyne metathesis), see, for instance:

10b Curini M. Epifano F. Maltese F. Rosati O. Synlett  2003,  552 

10c Rhee JU. Krische MJ. Org. Lett.  2005,  7:  2493 

10d Jin T. Yamamoto Y. Org. Lett.  2007,  9:  5259 

10e Bera K. Sarkar S. Biswas S. Maiti S. Jana U. J. Org. Chem.  2011,  76:  3539 

11 For the Lewis acid induced fragmentation of oxetanes prepared by Paterno-Büchi cycloaddition, see: Carless HJ. Trivedi HS. J. Chem. Soc., Chem. Commun.  1979,  382 

12 Gerbino DC. Mandolesi SD. Podesta JC. Schmalz H.-G. Eur. J. Org. Chem.  2009,  3964 

13 Silva LF. Siqueira FA. Pedrozo EC. Vieira FYM. Doriguetto AC. Org. Lett.  2007,  9:  1433 

14 Enders D. Niemeier O. Synlett  2004,  2111 

15

It proved to be important to quench the reaction mixture by addition of aq NaHCO₃ prior to extractive workup. Otherwise significant amounts of a by-product (a dimer of 17 as indicated by GC-MS) were formed probably through a proton-mediated process.

16a Poe SL. Cummings MA. Haaf MP. McQuade DT. Angew. Chem. Int. Ed.  2006,  45:  1544 

16b Baeyer A. Drewsen V. Ber.  1882,  15:  2856 

17

General Procedure for BF ₃ ˙Et ₂ O-Induced Ring-Closing Metathesis: In an argon-flushed Schlenk tube ortho-prenyl acetophenone (13a; 250 mg, 1.32 mmol) dissolved in anhyd CH₂Cl₂ (26 mL) was cooled to -40 ˚C. Dropwise addition of BF₃˙OEt₂ (0.25 mL, 1.98 mmol) afforded a yellow solution, which was stirred for 1 h at -40 ˚C. After addition of sat. aq NaHCO₃ (20 mL) at 0 ˚C the mixture was extracted with CH₂Cl₂ (3 × 40 mL). The combined organic layers were dried (MgSO₄), filtered and concentrated under reduced pressure. The residue was purified by chromatography on silica(cyclohexane) to provide 3-methyl-1H-indene (17; 150 mg, 1.15 mmol, 87%) as a colorless oil; R _f 0.65 (pentane). ^¹H NMR (300 MHz, CDCl₃): δ = 2.18 (dd, 3 H), 3.33 (m, 2 H), 6.21 (d, 1 H) 7.20 (dt, 1 H), 7.33 (q, 2 H), 7.46 (d, 1 H). ^¹³C NMR (75 MHz, CDCl₃): = 13.0, 37.6, 118.8, 123.6, 124.4, 126.0, 128.7, 139.9, 144.3, 146.1. IR-ATR:(film) = 3013 (w), 2931 (w), 1681 (m), 1460 (m), 1433 (m), 1379 (m), 1015 (m), 1001 (m), 943 (m), 760 (s), 717 (s) cm^-¹. HRMS (EI, 70 eV): m/z calcd for C₁₀H₁₀: 130.0782; found: 130.079.