Synlett 2004(1): 97-98  
DOI: 10.1055/s-2003-44994
LETTER
© Georg Thieme Verlag Stuttgart · New York

Annulations Using Phosphonium Salts and Enolate Anions - A Direct Route to Naphthalenes

George A. Kraus*, Prabir K. Choudhury
Department of Chemistry, Iowa State University, Ames, IA 50011, USA
e-Mail: gakraus@iastate.edu;
Further Information

Publication History

Received 19 August 2003
Publication Date:
17 December 2003 (online)

Abstract

Ketone enolates react with an aldehyde phosphonium salt to produce naphthalenes in a one-pot reaction

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To a freshly prepared solution of LDA (1 mmol in 3 mL of THF) was added the ketone (1 mmol) in 1 mL of THF dropwise at -78 °C and the reaction was stirred at -78 °C for 1 h. The cold solution was added via a cannula to the phosphonium salt (1 mmol) in 5 mL of THF at -78 °C. The solution was allowed to slowly warm to 0 °C. One-Pot Reaction: To the solution was then added 0.5 mL of concentrated HCl and was stirred at r.t. for 0.5-3 h (except for the adduct from cyclopentanone which required 10 h). The aqueous layer was extracted twice with Et2O. The combined organic layers were dried over MgSO4, filtered, concentrated in vacuo and purified by flash chromatography on silica gel using EtOAc:hexane.
Two-Step Reaction: To the solution was then added glacial acetic acid followed by water. The aqueous layer was extracted three times with EtOAc. The combined organic layers were dried over Na2SO4, filtered and concentrated in vacuo. To the alcohol in 4 mL of THF was added PTSA (0.25-0.50 equiv.) The reaction was stirred for 2-18 h. After aqueous workup, the crude product was purified by chromatography on silica gel using EtOAc:hexane.
Adduct from methyl hepten-2-one: 1H NMR (CDCl3): δ = 1.58 (s, 3 H), 1.69 (s, 3 H), 2.34-2.42 (m, 2 H), 2.79 (t, J = 8.1 Hz, 2 H), 5.18-5.23 (m, 1 H), 7.32-7.47 (m, 3 H), 7.62 (s, 1 H), 7.74-7.81 (m, 3 H). 13C NMR (CDCl3): δ = 17.9, 25.9, 30.1, 36.5, 123.9, 125.2, 126.0, 126.5, 127.6, 127.7, 127.8, 127.9, 132.1, 132.4, 133.8, 140.1. HMRS calcd for C16H18: 210.1408. Found: 210.1413.