A New LiBr-Catalyzed, Facile and Efficient Method for the Synthesis of 14-Alkyl or Aryl-14H-dibenzo[a,j]xanthenes and Tetrahydrobenzo[b]pyrans under Solvent-Free Conventional and Microwave Heating

Anil Saini; Sanjay Kumar; Jagir S. Sandhu

doi:10.1055/s-2006-947339

LETTER

A New LiBr-Catalyzed, Facile and Efficient Method for the Synthesis of 14-Alkyl or Aryl-14H-dibenzo[a,j]xanthenes and Tetrahydrobenzo[b]pyrans under Solvent-Free Conventional and Microwave Heating

Anil Saini, Sanjay Kumar, Jagir S. Sandhu*
Department of Chemistry, Punjabi University, Patiala 147 002, India
Fax: +91(175)2283073; e-Mail: j_sandhu2002@yahoo.com;

Abstract

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Abstract

An efficient method for the synthesis of 14-alkyl or aryl-14H-dibenzo[a,j]xanthenes and tetrahydrobenzo[b]pyrans under solvent-free conventional and microwave heating using lithium bromide, is described.

Key words

xanthenes - tetrahydrobenzo[b]pyrans - solvent-free - lithium bromide - microwave irradiation

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References and Notes

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General Procedure for the Synthesis of 14-Alkyl or Aryl Dibenzo[ a,j ]xanthenes - Method A.
A mixture of aldehyde (2 mmol), β-naphthol (4 mmol) and LiBr (0.3 mmol) were mixed and stirred for 5 min at r.t. and then temperature was raised to 130 °C and maintained for the appropriate time given in Table [1] . After completion of reaction (TLC), the reaction mixture was cooled to r.t. and H₂O (20 mL) was added and the mixture stirred for 5 min. The solid thus obtained was filtered and the crude product obtained was purified by recrystallization from EtOH.
Method B.
A mixture of aldehyde (2 mmol,), β-naphthol (4 mmol) and LiBr (0.3 mmol) were irradiated in a domestic microwave oven at 500 W for the appropriate time according to Table [1] . After completion of reaction (TLC), the reaction mixture was cooled to r.t. and H₂O (20 mL) was added and the mixture stirred for 5 min. The solid thus obtained was filtered and the crude product obtained was purified by recrystallization from EtOH.

General Procedure for the Synthesis of Tetrahydrobenzo[ b ]pyran - Method A.
A mixture of aldehyde (2 mmol,), 5,5-dimethyl-1,3-cyclo-hexanedione (2 mmol), active methylene compound (2 mmol) and LiBr (0.6 mmol) was mixed and stirred for 5 min at r.t. and then heated at 90 °C for the appropriate time given in Table [2] . After completion of reaction (TLC), the reaction mixture was cooled to r.t., H₂O (20 mL) was added and the mixture stirred for 5 min. The solid thus obtained was filtered and the crude product obtained was purified by recrystallization from EtOH.
Method B.
A mixture of aldehyde (2 mmol), 5,5-dimethyl-1,3-cyclo-hexanedione (2 mmol), active methylene compound (2 mmol) and LiBr (0.6 mmol) was irradiated in a domestic microwave oven at 500 W for the appropriate time according to Table [2] . After completion of reaction (TLC), the reaction mixture was cooled to r.t., H₂O (20 mL) was added and the mixture stirred for 5 min. The solid thus obtained was filtered and the crude product obtained was purified by recrystallization from EtOH.

<A NAME="RD03806ST-21A">21a</A> Wang XS. Shi DQ. Tu SJ. Yao CS. Synth. Commun. 2003, 33: 119

Selected Characterization Data. 14-Phenyl-14 H -dibenzo[ a,j ]xanthene (3a, Table 1, Entry 1).
Mp 184-85 °C. IR (KBr): 3030, 1612, 1242 cm^-1. ¹H NMR (200 MHz, CDCl₃): δ = 6.75 (s, 1 H), 7.10-8.10 (m, 17 H). Anal. Calcd for C₂₇H₁₈O: C, 90.47; H, 5.06. Found: C, 90.55; H, 5.15.
14-(4-Methoxyphenyl)14- H -dibenzo[ a,j ]xanthene (3c, Table 1, Entry 3).
Mp 203-04 °C. IR (KBr): 3035, 1621, 1581, 1252. cm^-1. ¹H NMR (200 MHz, CDCl₃): δ = 3.50 (s, 3 H), 6.45 (s, 1 H), 6.73 (d, J = 9.3 Hz, 2 H), 7.36-7.92 (m, 12 H), 8.36 (d, J = 9.3 Hz, 2 H). Anal. Calcd for C₂₈H₂₀O₂: C, 86.57; H, 5.19. Found: C, 86.35; H, 5.29.
14-(3-Bromophenyl)-14- H -dibenzo[ a,j ]xanthene (3d, Table 1, Entry 4).
Mp 190-92 °C. IR (KBr): 3040, 1613, 1245. cm^-1. ¹H NMR (200 MHz, CDCl₃): δ = 6.62 (s, 1 H), 7.21-20 (m, 16 H). Anal. Calcd for C₂₇H₁₇BrO: C, 74.15; H, 3.92. Found: C, 74.21; H, 3.86. UV (CHCl₃): λ_max = 245, 266, 335 nm.
14-(4-Nitrophenyl)-14 H -dibenzo[ a,j ]xanthene (3g, Table 1, Entry 7).
Mp 309-10 °C. IR (KBr): 3070, 1615, 1540, 1355, 1245. cm^-1. ¹H NMR (200 MHz, CDCl₃): δ = 7.20-7.90 (m, 12 H), 8.15 (d, J = 9.0 Hz, 2 H), 8.55 (d, J = 9.0 Hz, 2 H). Anal. Calcd for C₂₇H₁₇NO₃: C, 80.38; H, 4.25; N, 3.47. Found: C, 80.29; H, 4.10; N, 3.55. UV (CHCl₃): λ_max 245, 259, 335 nm.
14-(4-Methylphenyl)-14 H -dibenzo[ a,j ]xanthene (3i, Table 1, Entry 9).
Mp 227-29 °C. IR (KBr): 3038, 1618, 1240 cm^-1. ¹H NMR (200 MHz, CDCl₃): δ = 2.30 (s, 3 H), 6.55 (s, 1 H), 7.15-7.95 (m, 16 H). Anal. Calcd for C₂₈H₂₀O: C, 90.29; H, 5.41. Found: C, 90.41; H, 5.49.
14-Ethyl-14 H -dibenzo[ a,j ]xanthene (3j, Table 1, Entry 10).
Mp 112-13 °C. IR (KBr): 3045,2901, 1615, 1221 cm^-1. ¹H NMR (200 MHz, CDCl₃): δ = 0.98 (t, J = 6.1 Hz, 3 H) 1.64 (d, J = 6.1 Hz, 3 H), 5.60 (q, J = 6.1 Hz, 1 H) 7.09-7.97 (m, 12 H). Anal. Calcd for C₂₃H₁₈O: C, 89.00; H, 5.85. Found: C, 89.12; H, 5.76.
2-Amino-3-cyano-4-phenyl-7,7-dimethyl-5-oxo-4 H -5,6,7,8-tetrahydrobenzo[ b ]pyran (6a, Table 2, Entry 1).
Mp 232-234 °C. IR (KBr): 3392, 3288, 2934, 2198, 1685, 1601 cm^-1. ¹H NMR (200 MHz, CDCl₃): δ = 0.97 (s, 3 H), 1.04 (s, 3 H), 2.18 (d, J = 14.5 Hz, 1 H), 2.23 (d, J = 14.5 Hz, 1 H), 2.50-2.60 (br s, 2 H), 4.30 (s, 1 H), 6.10 (s, 2 H), 7.20-7.40 (m, 5 H). Anal. Calcd for C₁₈H₁₈N₂O₂: C, 73.45; H, 6.16; N, 9.52. Found: C, 73.58; H, 6.08; N, 9.40.
Ethyl-2-Amino-4-phenyl-7,7-dimethyl-5-oxo-4 H -5,6,7,8-tetrahydrobenzo[ b ]pyran Carboxlate (6d, Table 2, Entry 4).
Mp 191-193 °C. IR (KBr): 3420, 2960, 2925, 1749, 1598, 1358 cm^-1. ¹H NMR (200 MHz, CDCl₃): δ = 1.0 (s, 3 H), 1.06 (s, 3 H), 1.21 (t, J = 7.5 Hz), 2.14 (d, J = 14.0 Hz, 1 H), 2.25 (d, J = 14.0 Hz, 1 H), 2.49 (br s, 2 H), 4.19 (q, J = 7.5 Hz), 4.27 (s, 1 H), 5.84 (s, 2 H), 7.10-7.35 (m, 5 H). Anal. Calcd for C₂₀H₂₃NO₄: C, 70.38; H, 6.74; N, 4.11. Found: C, 70.30; H, 6.83; N, 4.07.