A series of related 6,7-dibromoindole compounds were prepared to study the effects of pyrrole and benzene ring substitution patterns on the regioselectivity of 6,7-indole aryne cycloadditions with 2-tert-butylfuran. The arynes were generated by our metal-halogen exchange/elimination protocol (see for example Buszek, Luo et al., Org. Lett. 2007 , 9, 4135; Buszek, Brown et al., Org. Lett. 2009 , 11, 201; Brown, Luo et al., Tetrahedron Lett. 2009 , 50, 63; Brown and Buszek, Tetrahedron Lett. 2012 , 53, 4022; Chandrasoma, Brown et al., Tetrahedron Lett. 2013 , 54, 913). The results of this investigation (see Garr, Luo et al., Org. Lett. 2010 , 12, 96 for our initial computational studies) reveal that substitution at the 3-position on the indole ring in particular results in remarkable regiocontrol that favored the contrasteric products. Aromatic conjugation at this site significantly enhanced this effect. However, the presence of most 4- or 5-substituents generally resulted in markedly reduced selectivity. Exceptions in this latter series included the 4-ethyl and 4-iodo cases both of which also gave predominantly contrasteric products even in the absence of a beneficial C-3 substituent.

Further investigations into the regioselectivity of 6,7-indole aryne cycloadditions with 2-substituted furans: Remarkable contrasteric preference depends on pyrrole and benzene ring substitution

247th National Meeting (2014)

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