Benzo[c]furans

Gain or loss of aromaticity in Diels–Alder transition states and adducts: a theoretical investigation

“…The dienes and dienophiles known thus far can be broadly classified as simple, substituted and masked dienes and dienophiles. 3,4 While simple and substituted addends have expressed functionality, the masked dienes or dienophiles have hidden functionality. The mechanisms of the reactions involving the latter type of addends are complicated in the sense that, as the reacting group is a part of the whole system, the remaining part of the system reacts to changes in the functionality during the reaction and can thus influence the reaction course to a larger extent.…”

“…Masked dienes and dienophiles of various kinds have been the subject of several experimental reports 3,4 and have been studied particularly with regard to various stereochemical aspects. Masked dienes and dienophiles can be of cumulated, ring-fused, cage-fused types, etc.…”

Selective Halogen-Lithium Exchange of 1,2-Dihaloarenes for Successive [2+4] Cycloadditions of Arynes and Isobenzofurans

“…The residue was purified by PTLC (hexane/EtOAc = 8/2) to give 2,3-dibromo-9,10-dihydro-9,10-epoxyanthracene (6a, 67.9 mg, 78.1%) as a white solid and 2,3-dibromo-5,7,12,14-tetrahydro-5,14:7,12-diepoxypentacene (7a, 1.2 mg, 1.0%, ds: 17/83) as a mixture of diastereomers. (10). According to the procedure described for the synthesis of cycloadduct 6a, 1-bromo-2-iodobenzene (8a, 112 mg, 0.396 mmol), isobenzofuran 9a (129 mg, 0.301 mmol) and n-BuLi (1.60 M in n-hexane, 0.25 mL, 0.40 mmol) gave, after purified by silica-gel flash column chromatography (hexane/CH2Cl2/Et2O = 98/1/1→96/3/1), cycloadduct 10 (110 mg, 72.4%) as a white solid.…”

“…We previously reported dual annulations of dibromoisobenzofuran 1, a formal equivalent of didehydroisobenzofuran A, via [2+4] cycloadditions of aryne [1][2][3][4][5][6][7][8][9] and isobenzofuran [10][11][12][13][14][15][16][17][18][19][20][21][22][23] (Scheme 1). Selective bromine-lithium exchange from the starting two dibromides 2 and 3 enables the tandem generation of arynes and dual cycloadditions with two different arynophiles (step 1 and step 2).…”

Preparation and cycloaddition chemistry of 1-amino substituted isobenzofurans

“…5 Since these heteroaromatic ring systems are highly reactive as Diels-Alder dienes, they are commonly generated in the presence of a dienophilic trap. While examples of 1-alkyl and 1-aryl substituted isobenzofurans are common 6,7 there are only a few citations in the literature that involve amino-substituted isobenzofurans. [8][9][10] Our interest in preparing various benzo[c]phenanthridinium salts (2) as antitumor agents 11 as well as the benzophenanthridine alkaloid corynoline (4) 12 led us to explore their syntheses via the intramolecular Diels-Alder reaction of an amino substituted isobenzofuran 13 as illustrated in Scheme 1.…”