Preparation of Isobenzofuran-Aryne Cycloadducts

Article abstract of DOI:10.1021/jo00215a031

A one-pot procedure is described for carrying out the sequence 1,4-elimination of acetal 1 to form isobenzofuran; the formation of 1,3-dilithioisobenzofuran; the conversion to 1,3-bis(trimethylsilyl)isobenzofuran (5); the generation of arynes and cycloaddition to 5.This method allows the use of lithium tetramethylpiperidide induced dehydrohalogenation of haloaromatics to generate the arynes, a procedure which fails with unsilylated isobenzofuran due to the acidity of the 1,3-protons.The protiodesilylation of the cycloadducts occurs with surprising ease, upon treatmentwith either tetraalkylammonium fluoride/THF or base (potassium tert-butoxide or KOH) in Me2SO, to furnish the novel unsubstituted isobenzofuran-aryne adducts.Three examples are given, utilizing benzyne, 1-naphthalyne, and 3-pyridine.Procedures for subsequent deoxygenation of the cycloadducts to anthracene, benzanthracene, and benzisoquinoline, respectively, are described.The cycloadduct precursor of benzanthracene is shown to undergo highly regioselective reduction on treatment with lithium tri-tert-butoxyaluminohydride/triethylborane, with preferential attack occurring at the more accessible 7-position.