Benzo furan synthesis

H-Benzo[a]carbazole, 4,4a,5,l 1,1 la,l Ib-hexahydro-synthesis, 4, 283 Benzo[b]carbazole, N-acetyl-photochemical rearrangements, 4, 204 Benzo[/]chroman-4-one, 9-hydroxy-2,2-dimethyl-synthesis, 3, 851 Benzochromanones synthesis, 3, 850, 851, 855 Benzochromones synthesis, 3, 821 Benzocinnoline-N-imide ring expansion, 7, 255 Benzocinnolines synthesis, 2, 69, 75 UV, 2, 127 Benzocoumarins synthesis, 3, 810 Benzo[15]crown-5 potassium complex crystal stmcture, 7, 735 sodium complex crystal stmcture, 7, 735 Benzo[ 18]cr own-6 membrane transport and, 7, 756 Benzo[b]cyclohepta[d]furans synthesis, 4, 106 Benzocycloheptathi azoles synthesis, 5, 120... 

A palladium-catalyzed one-step synthesis of dihydrobenzo[fc]furan-based fused aromatic heterocycles from bifunctional bromoenoates or bromoalkyl indoles and iodoarenes was reported, and an example is provided in the scheme below <060L3601>. 2-Alkyl- or 2-aryl-substituted benzo[ >]furans were synthesized by a copper-TMEDA catalyzed intramolecular annulation from the corresponding ketones <06OL1467>. 

In order to exploit the cycloaddition reactions of 2-vinylbenzofurans for natural product synthesis, the reactions of (E)-2-()S-methoxyvinyI)benzo-furans have been examined. The simplest compound (139, Scheme 36) on reaction with dimethyl acetylenedicarboxylate in boiling toluene gave a mixture of products. The major adduct was not the one expected but was its conjugation product 140. The diene system in 140 is able to react with... 

Numerous examples of natural products with the benzo[ ]furan nucleus have been identified. It occurs under many guises dibenzofurans, /3-coumaranones, a-pyranobenzo[6]furans, y-pyranobenzo[6]furans, and the spiro-2,3-dihydrobenzofurans such as griseofulvin. Many of the natural benzo[6]furans have physiological, pharmacological and toxic properties and as a result an active interest exists in their chemical synthesis. 

In the following scheme, the benzo[Z>]furan core of ( )-frondosin B was built up by the palladium-catalyzed quinone reduction, followed by Lewis acid-mediated benzo[Z>]furan formation <07OL3837>. In the total synthesis of bisabosquals, the core structure of benzo[ ]furan was constructed by an epoxide-ring opening reaction <07T10018>. 

Fischer-type chromium carbene complexes of furans underwent Dotz benzannulation with alkynes to provide trisubstituted benzo [, ]furan derivatives. An example used in the synthesis of isodityrosine is depicted in Equation (39) <2005JOC7422>. The efficiency of the reaction could be improved by ultrasound sonication <19990L1721>. 

Benzo[ ]furan-based diazobutenoates were used as a substrate to make a cyclopropane in 89% yield via a rhodium-catalyzed intramolecular process, as can be seen in Equation (74). Cyclopropane 88 was the key intermediate for the total synthesis of diazonamide A <20000L3521>. 

As illustrated in Equation (77), the regioselective nitration of 2-(trimethylstannyl)benzo[/)]furan was also applied to the synthesis of 2-nitrobenzo[ ]furan. The reaction proceeded by an initial treatment of benzo[ ]furan 82 with -BuLi/ MesSnCl, and was then followed by reaction with tetranitromethane (TNM) or dinitrogen tetroxide <2003EJ01711>. 

An efficient approach for asymmetric syntheses of benzo[ ]furan-l-alkylamines was developed by reaction of 2-lithiated benzoMfuran with aldehyde-SAMP-derived hydrazones (SAMP = (3 )-(—)-l-amino-2-methoxymethyl-pyrolidine Equation 84). In this way, an efficient synthesis of hydrazine 91 was achieved <2004TA747>. 

In the total synthesis of naturally occurring frondosin B, the palladium-catalyzed coupling reaction of C-3 stannylated benzo[. ]furan 94 with the vinyl triflate 95 was employed as a key step to build up the framework of the final target, as depicted in Equation (89) <2001JA1878>. 

The palladium-catalyzed Suzuki-Miyaura reaction of 3,5-dibromo-2-pyronc 100 with benzo[, ]furan-2-boronic acid 101 was applied to the synthesis of 3-(benzo[ ]furan-2-yl)-5-bromo-pyrone 102 in 50% yield (Equation 92) <2004SL2197>. 

The palladium-catalyzed hydrofuranylation of alkylidenecyclopropane 105 with unfunctionalized benzo[ ]furan was utilized in the synthesis of a 2-allylbenzo[ ]furan derivative 106, as illustrated in Equation (96) <2000JA2661>. 

Chloromercurio-benzo[ ]furans 107 were key intermediates for the syntheses of natural product XH14 and its analogs. The synthesis proceeded by the palladium-catalyzed carbonylation reaction as a pivotal step. The 3-chloromercurio-benzo[ ]furan 107 was also reduced to form its hydride derivative by NaBH4 reduction, as illustrated in Scheme 54 <2002JOC6772>. 

As can be seen in Scheme 58, a new synthesis of 7-lactams was also achieved by reaction of benzo[, ]furan-derived vinyl sulfilimines with dichloroketene, a reaction which proceeded through a [3,3] sigmatropic rearrangement <20050L839>. 

Benzo[/ ]furyl-4-chloromethyl-l,3-oxazole 127, an important intermediate for the synthesis of potent and highly selective D3 receptor ligands, was realized by a direct condensation of benzo[/ ]furan-2-carbamide and 1,3-dichloro-propan-2-one (Equation 108) <2003JME3822>. 

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