Reaction of Benzyne with Styrene Oxide: Insertion of Arynes into a C-O Bond of Epoxides

Abstract

Benzyne inserts into one of the C-O bonds of styrene ­oxide to form a dihydrobenzofuran as the major product together with five other reaction products. A detailed study of the reaction mixture clarified an intriguing forty-year-old personal communication from Stiles and Haag.

arynes - epoxides - furans - insertions - ring expansion

References and Notes

<A NAME="RD40206ST-1">1</A>

Current address: Department of Chemistry, University of York, Heslington, York YO10 5DD, UK.

<A NAME="RD40206ST-2A">2a</A> Himeshima Y. Sonoda T. Kobayashi H. Chem. Lett.  1983,  1211 

<A NAME="RD40206ST-2B">2b</A> Peña D. Cobas A. Pérez D. Guitián E. Synthesis  2002,  1454 

For some recent representative examples, see:

<A NAME="RD40206ST-3A">3a</A> Yoshida H. Tanino K. Ohshita J. Kunai A. Angew. Chem. Int. Ed.  2004,  43:  5052 

<A NAME="RD40206ST-3B">3b</A> Tambar UK. Stoltz BM. J. Am. Chem. Soc.  2005,  127:  5340 

<A NAME="RD40206ST-3C">3c</A> Liu Z. Larock RC. J. Am. Chem. Soc.  2005,  127:  13112 

<A NAME="RD40206ST-3D">3d</A> Lin W. Sapountzis I. Knochel P. Angew. Chem. Int. Ed.  2005,  44:  4258 

<A NAME="RD40206ST-4">4</A> For a recent highlight, see: Peña D. Pérez D. Guitián E. Angew. Chem. Int. Ed.  2006,  45:  3579 

<A NAME="RD40206ST-5">5</A> Stiles M. Burckhardt U. Haag A. J. Org. Chem.  1962,  27:  4715 

<A NAME="RD40206ST-6">6</A> Recently Yoshida et al. reported the insertion of arynes into the C=O double bond of aldehydes: Yoshida H. Watanabe M. Fukushima H. Ohshita J. Kunai A. Org. Lett.  2004,  6:  4049 

<A NAME="RD40206ST-7">7</A> Hoffmann RW. Dehydrobenzene and Cycloalkynes   Academic Press; New York: 1967. 

<A NAME="RD40206ST-8">8</A>

Stiles, M.; Haag, A. personal communication in reference 7 (page 178).

<A NAME="RD40206ST-9">9</A>

General procedure for the reaction of triflate 5 with styrene oxide (6): In a Schlenk tube equipped with a septum and a magnetic stirring bar, a mixture of triflate 5 (242 µL, 1.00 mmol), styrene oxide (6, 228 µL, 2.00 mmol) and CsF (304 mg, 2.00 mmol) was stirred in MeCN (15 mL) for 24 h. The resulting mixture was concentrated under reduced pressure and the residue was purifed by column chromatography (SiO₂; CH₂Cl₂-hexane, 1:99 to 50:50) to afford compounds 7 and 9-12. All of the products gave satisfactory NMR (¹H, ¹³C) and MS. Selected data for 7: [10] ¹H NMR (250 MHz, CDCl₃): δ = 7.36-7.14 (m, 6 H), 7.02 (m, 1 H), 6.90-6.82 (m, 2 H), 4.90 (dd, J = 9.4, 8.7 Hz, 1 H), 4.67 (dd, J = 9.2, 7.3 Hz, 1 H), 4.42 (dd, J = 8.6, 7.3 Hz, 1 H); ¹³C NMR (62.8 MHz, CDCl₃): δ = 160.2 (C), 142.8 (C), 130.5 (C), 128.8 (2CH), 128.5 (CH), 127.8 (2CH), 127.0 (CH), 125.2 (CH), 120.8 (CH), 109.6 (CH), 79.1 (CH₂), 48.5 (CH); MS (EI): m/z (%): 196 (100). GC/MS were performed on an Agilent 6890N/5973 inert instrument with a HP-5MS capillary column (25 mm × 30 m × 25 mm; 70 to 300 °C, 30 °C/min).

<A NAME="RD40206ST-10">10</A> Arnold DR. Fahie BJ. Lamont LJ. Wierzchowski J. Young KM. Can. J. Chem.  1987,  65:  2734 

<A NAME="RD40206ST-11">11</A>

This mechanism is the same as that proposed in reference 8.

<A NAME="RD40206ST-12">12</A>

The use of other epoxides such us cyclohexene oxide or propylene oxide did not afford the corresponding insertion products.

<A NAME="RD40206ST-13">13</A> There is only one example of the insertion of arynes into element-element sigma bonds of cyclic molecules, in particular five- and six-membered-ring disilanes, see: Yoshida H. Ikadai J. Shudo M. Ohshita J. Kunai A. Organometallics  2005,  24:  156