D. Park, S. Gowrisankar, Jae Nyoung Kim
Feb 7, 2006
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0
Influential Citations
18
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Journal
ChemInform
Abstract
Dihydrobenzofuran derivatives are important synthetic intermediates and showed many biologically interesting activities. However, synthetic methods for the compounds are rather limited. Recently Trost and co-workers have reported the synthesis of dihydrobenzofuran derivatives starting from the Baylis-Hillman adducts by using the reductive Heck-type cyclization strategy. Very recently, Lamaty and co-workers reported the synthesis of 3,3disubstituted-2,3-dihydrobenzofuran derivatives via palladium-catalyzed cascade allylation-carbopalladation-Suzuki cross coupling strategy. On the other hand, Shanmugam and Rajasingh have reported the synthesis of tetrahydrofuran backbone by the radical cyclization of triple bond containing cinnamate derivatives, which were synthesized from the BaylisHillman adducts. They used vinyl radical, which was formed via the in situ hydrostannylation of triple bond. We were stimulated by the results and envisioned that we could prepare 2,3-dihydrobenzofuran skeleton if we use aryl radical instead of the vinyl radical as shown in Scheme 1. Thus, we prepared the starting material 3a from the reaction of the acetate of Baylis-Hillman adduct 1a and 2bromophenol (2a) as shown in Scheme 1. The starting material 3a was converted to the desired 2-benzyl-2,3dihydrobenzofuran-2-carboxylic acid methyl ester (4a), the 5-exo-trig cyclization product, in 79% yield under the influence of n-Bu3SnH/AIBN in benzene at refluxing temperature (entry 1 in Table 1). We could not isolate the corresponding dihydrobenzopyran derivative, the 6-endotrig cyclization product, or simple reduction product. The optimum amounts of n-Bu3SnH and AIBN were studied and