“…Thus, metalation of benzofuran and quenching with trimethylsilyl chloride gave 2-trimethylsilylbenzofuran ( 1 ) in high yield. A second metalation , with an iodine quench afforded crude 7-iodo-2-trimethylsilylbenzofuran ( 2 ) which, on ozonolysis, gave the desired iodoaldehyde 3 (Scheme ). 2 Preparation of 3-Iodosalicylaldehyde…”
[reaction: see text] Tributyltin hydride mediated addition of 3-iodosalicylaldehyde to benzene in the presence of catalytic benzeneselenol affords (1,4-cyclohexadien-3-yl)salicylaldehyde. Homologation of the aldehyde group is followed by cycloetherification with dimethyl dioxirane to give a 4,6-disubstituted tetrahydrodibenzofuran. Adjustment of oxidation states and introduction of a second chain by Wittig olefination affords the beta-sheet initiator, ethyl 4-(2-tert-butoxycarbonylaminoethyl)-6-dibenzofuranpropanoate.
“…Thus, metalation of benzofuran and quenching with trimethylsilyl chloride gave 2-trimethylsilylbenzofuran ( 1 ) in high yield. A second metalation , with an iodine quench afforded crude 7-iodo-2-trimethylsilylbenzofuran ( 2 ) which, on ozonolysis, gave the desired iodoaldehyde 3 (Scheme ). 2 Preparation of 3-Iodosalicylaldehyde…”
[reaction: see text] Tributyltin hydride mediated addition of 3-iodosalicylaldehyde to benzene in the presence of catalytic benzeneselenol affords (1,4-cyclohexadien-3-yl)salicylaldehyde. Homologation of the aldehyde group is followed by cycloetherification with dimethyl dioxirane to give a 4,6-disubstituted tetrahydrodibenzofuran. Adjustment of oxidation states and introduction of a second chain by Wittig olefination affords the beta-sheet initiator, ethyl 4-(2-tert-butoxycarbonylaminoethyl)-6-dibenzofuranpropanoate.
“…[23a,28-29] However, when used in THF at À 15 °C for 1 h, the only compound formed after iodolysis was the known 2-(3,4,5-trimethoxybenzoyl)benzofuran [30] (3; Figure 1, left), isolated in 27 % yield. Since sec-butyllithium-TMEDA has already been used to deprotometallate 2,3-diphenylbenzofuran in THF (À 78 °C for 1 h), [31] we also tested this combination (3 equiv) on the lithium salt in THF; however, even after 6 h of basesubstrate contact at 0 °C before iodolysis, the alcohol 2 was again mostly recovered. Without TMEDA, treatment with secbutyllithium (1.1 equiv) in THF at À 15 °C for 0.5 h followed by addition of iodine not only resulted in the recovery of 2 (~60 %) but also provided an unidentified product.…”
When 2-iodobenzofuran was treated sequentially with lithium 2,2,6,6-tetramethylpiperidide in tetrahydrofuran at À 50 °C and an aldehyde, the 2-substituted 3-iodobenzofuran resulting from the halogen dance was the only isolated product. However, from 2-iodobenzothiophene, these conditions led to mixtures in which the 2-substituted 3-iodobenzothiophene was always accompanied by the 2-substituted benzothiophene. The use of 2-bromobenzothiophene as a catalyst made it possible to significantly reduce this competitive dehalogenation. To confirm the halogen dance reaction, the products were unambiguously synthesized by using direct halogenations and deprotolithiation-trapping sequences as key steps. Our efforts to access 2,7-disubstituted and 7-substituted derivatives of benzofuran and benzothiophene have also been reported.
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