Chemoselective reduction of unsaturated •- and •-lactones by sodium borohydride in the presence of triethylamine in THF
Morteza Bidar,a* Gayane Tokmajyan,a Farough Nasiri,b and Aida Avetisyana
aDepartment of Chemistry, Yerevan State University, 1A Manukyan Str. 0025 Yerevan, Armenia
bDepartment of Chemistry, University of Kurdistan, PO Box 66177-416, Sanandaj, Iran
E-mail:
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Abstract
•,•-Unsaturated •- and •-lactones were selectivity reduced to the corresponding saturated lactones and oxospiro systems respectively using sodium borohydride in the presence of triethylamine in THF, in excellent yields.
Keywords: Conjugate reduction, •,•-unsaturated lactones, sodium borohydride, spiro lactones
Introduction
It is well known, that many saturated lactones are displaying interesting biological activities and can be used in many various areas, especially, in medicine, pharmacology, perfume making, pesticides etc. Artemisinin and Santonin, endowed with valuable biological activity, are compounds containing saturated •- and •-lactone rings.1,2 Many compounds, such as pilocarpine, a cholinergic drug, are also derivatives of •-butanolides. Subsequent investigations, in the area of the synthesis of new derivatives of saturated •-lactones are of great interest and can have a valuable potential for new biologically active compounds.3
Therefore, reduction of functionalized unsaturated lactones can be useful method for synthesizing functionalized saturated lactones, which would be otherwise difficult -if not impossible- to obtain.4 There are known methods for synthesizing •-butanolide, based on various organic oxides,4 but unfortunately these reagents are not readily available.
Synthesis of functionalized unsaturated •-lactones from 2,3-substitued •-hydroxy ketones and compounds with active methylene group is well documented and can easily be extended to the synthesis of unsaturated •-lactones through double bond reduction with various reagents.5 Catalytic hydrogenation is not always possible to apply because of unavailability of necessary catalysts and hydrogen hazards.6 On the other hand, the reduction of butenolides by complex metal hydrides (LiAlH4, NaBH4) opens the lactone rings for production of the corresponding glycols.7,8
