Improved Synthesis of Benz[a]acephenanthrene

Abstract

A convenient, three-step synthesis of benz[a]acephenanthrene (6) from commercially available materials is described.

Key words

Wittig reaction - photocyclization - benz[a]acephenantrene

References

• For recent reviews see:
• 1a Rabideau PW. Sygula A. Acc. Chem. Res.  1996,  29:  235 
• 1b Scott LT. Pure Appl. Chem.  1996,  68:  291 
• 1c Mehta G. Rao HSP. Tetrahedron  1998,  54:  13325 
• 1d Scott LT. Bronstein HE. Preda DV. Amselms RBM. Bratcher MS. Hagen S. Pure Appl. Chem.  1999,  71:  209 
• 2 Magnus P. Morris JC. Lynch V. Synthesis  1997,  506 
• 3 Marcinow Z. Rabideau PW. J. Org. Chem.  2000,  65:  5063 
• 4 Phillips DD. Chatterjee DN. J. Am. Chem. Soc.  1958,  80:  4364 
• 5 Becker CL. McLaughlin ML. Synlett  1991,  9:  642 

6

A solution of NaOEt in EtOH (12 mmol of Na in 50 mL EtOH) was added slowly to a boiling solution of the benzyltriphenylphosphonium bromide (10 mmol) and 4 (1.82 g; 10 mmol) dissolved in 10 mL of EtOH/benzene (1:1). The mixture was refluxed for 1 h and then kept at room temperature overnight (stirring). The product was purified by column chromatography with hexane to give 1.38 g (54%) of cis and trans isomers of 5 (M⁺ 256); separation of the mixture was not attempted.

7

A solution of 5 (0.512 g, 2 mmol) and 30 mg of iodine in cyclohexane (300 mL) was irradiated with a 200 W high pressure quartz Hg-vapor lamp for 2 h. Evaporation of the solvent provided a single product (by NMR and GC/MS) which was purified by column chromatography with hexane to give 0.42 g (83%) of a pale yellow solid 6: mp 118-120 °C (lit. [4] 115-118 °C); ¹H NMR (300 MHz, CDCl₃) δ 9.25 (d, J = , 8.4 Hz, 2 H), 7.98 (d, J = 7.8 Hz, 2 H), 7.71 (s, 2 H), 7.68-7.64 (m, 4 H), 3.45 (s, 4 H); ¹³C NMR (75.4 MHz, CDCl₃) δ 143.4, 137.89, 135.77, 129.75, 129.27, 127.06, 125.87, 125.7, 124.89, 121.87, 29.90; MS (EI, 70 eV) m/z (rel. intensity) 254 (100).