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Synlett 2006(12): 1928-1932  
DOI: 10.1055/s-2006-947339
LETTER
© Georg Thieme Verlag Stuttgart · New York

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;
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Publication History

Received 8 May 2006
Publication Date:
24 July 2006 (online)

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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

19

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.

20

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.