1,3-Diphenylisobenzofuran Diels-Alder cycloadduct

Based on the high dienophilicity of acyclic vinyl sulfones one should expect thiete dioxides to exhibit similar properties. Indeed, several Diels-Alder (2 + 4) cycloadditions with thiete dioxide as dienophile are known. For example, 1,3-butadiene and 1,3-diphenylisobenzofuran react with 3-chloro- or 3-bromo-thiete dioxides to afford the corresponding 1 1 Diels-Alder cycloadducts (equation 105). 

Density functional theory computational studies have been used to determine die importance of secondary orbital interactions for the stability of transition-state structures for die 4 + 2-cycloaddition of furan with cyclopropene.175 Kinetic studies of die 2 + 4-cycloaddition of 2-cyclopropylidene acetates with furan and dimethylful-vene suggest a mechanism involving diradicals or zwitterions as intermediates.176 Cyclopropene, produced by die reaction of allyl chloride with sodium bis(bimediyl-silyl)amide, reacts with 1,3-diphenylisobenzofuran to produce both endo- and exo-Diels-Alder cycloadducts isolated for the first tune.177... 

The intramolecular Diels-Alder cycloadditions of 1-aminobenzofurans provide a simple synthesis of benzo[/r]quinolines. A-Acetyl-2-azetine undergoes facile 4-1-2-cycloaddition with cyclopentadiene, 5,5-dimethoxy-1,2,3,4-tetrachlorocyclopentadiene, hexachloropentadiene, and diphenylisobenzofuran to produce exclusively endo-cyc o-adducts. The highly strained cyclic alkyne bicyclo[2.2.1]hept-2-en-5-yne (108), prepared from the heptavalent iodine precursor (107), has been trapped using 1,3-diphenylisobenzofuran to yield the adduct (109) (Scheme 41). The reaction of sodium dinitroxytrioxide (110) with 1,3-diphenylisobenzofuran gives an initial 4-1-2-cycloadduct (111), which rearranges to the final product (112) (Scheme 42). " The... 

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