Reactions with benzyne

Kuzuya M., Noguchi A. The Nature of Substituent Effects on Tautomeric Equilibria of 2-Pyridones and Their Reactions Trends Org. Chem. 1991 2 73-92 Keywords chemo- and regiochemistry of Diels-Alder reactions with benzyne,... 

Benzyne reacts with 7-dehydrocholesteryl methyl ether to form the ene products (110) and (111, X = H), while with tetrafluorobenzyne we isolated the anticipated cyclo-adduct (112) in addition to an ene product (111, X = F) 152>. We expected that less crowding would obtain in the transition states leading to cyclo-adducts from cholesta-2,4-diene, and obtained from a reaction with benzyne both the a- and 3-adducts (113, X = H) and (114). In a reaction with tetrafluorobenzyne we only obtained the a-adduct (113, X = F). 

The 7r-nature of the central bond in bicyclo[1.1.0]bulane is aptly demonstrated by its cycloaddition reaction with benzyne in 1,2-dichloroethane, from which two compounds 29 and 30 were isolated in moderate yield in a ratio of 6 1. The structures of the major and the minor compounds were identified as 3-phenylcyclobutene (29) and benzobicyclo[2.2.1]hex-2-ene (30), respectively.44 Deuterium labeling experiments showed that both products resulted from attack on bicy-clo[1.1.0]butane from the endo side.44... 

Vinylbenzo[6]thiophene undergoes Diels-Alder reactions with benzyne,468 maleic anhydride,469 benzo[6]thiophene-1,1-dioxide,469 p-benzoquinone, and various 1,4-naphthaquinones.469,470 With quinones, the product depends on the reaction conditions. For... 

One example is the reaction with benzyne of 3-vinylbenzo[/ ]thiophene 102, prepared by dehydration of 2-(3-benzo[b]thienyl)ethanol, to give 11-thiabenzo[a]fiuorene 103 (65AJC1781). 

The reaction of the sodium derivative of methylpyrazine with alkyl halides in liquid ammonia gives good yields (44-81%) of mono-alkylated products phenylation has been achieved by reaction with benzyne (generated from bromobenzene and sodamide in liquid ammonia) and gives 53% benzylpyrazine.178 The alkylation of the sodio derivative of 2-methoxy-3-methylpyrazine with methyl iodide, and of the product with ethyl bromide, gives 2-methoxy-3-sec-butylpyrazine (25) a constituent of galbanum oil.31... 

Other cyclopropenes have also been shown to act as the enophile or the ene thus (99) is converted to (100) in reasonable yield by reaction with benzyne 94), and (101) is converted to the diastereoisomers of (102) on heating with trans-2-butene for 11 h at 80 °C. The major product is believed to be (a), resulting from pseudo-exo-approach as in (103)95). 

Spirodienones are attractive intermediates for the preparation of calixarenes in which the intraanular hydroxy groups are partly replaced by hydrogen,93 amine 93 methyl,94 or halogen.95 The reaction with benzyne affords Diels-Alder adducts in high diastereofacial selectivity.92 No special use has been made of their chirality, however. 

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