Nitrostyrenes Friedel-Crafts alkylation

Figure 6.46 (A) Hydroxy-protected thiourea 141 and 142 lacking the hydroxy function and their catalytic efficiency in the Friedel-Crafts alkylation of indole with frans-P-nitrostyrene (139 78% yield 85% ee under identical conditions). (B) Proposal for the key hydrogen-bonding interactions between 139 and the model substrates.

Scheme 4.55 Enantioselective conjugate Friedel-Crafts alkylation of pyrroles with nitrostyrenes catalyzed by 60d.

The Friedel-Crafts alkylation of furans with P-nitrostyrene was promoted by lithium perchlorate in diethyl ether (13TL6776). 

Scheme 3.4 Friedel-Crafts alkylation of indole with nitrostyrene.

On the other hand, 2-naphthols have been used with different success as Michael donors in conjugate Friedel Crafts reactions with nitroalkenes and related substrates (Scheme 4.53). For example, cinchonine-derived thiourea 72b was identified as an excellent promoter for the reaction of a wide variety of 2-naphthols and nitroolefins, providing excellent yields and enantioselectivities. Remarkably, the more challenging p-alkyl substituted nitroalkenes were also found to undergo the reaction in a highly stereoselective way and with comparable yields to those obtained when nitrostyrene derivatives were employed. 

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