Miscellaneous Electrophilic Cyclizations

As is the case with miscellaneous nucleophilic cyclizations (Chapter 21), several electrophilic cyclizations leading to the indole ring do not appropriately fit into any of the preceding chapters in this category. As with the aforementioned chapter, 1 will mention the anthor of each new electrophilic indoliza-tion becanse fnture work might elevate that reaction to Name statns. As with all ionic reactions, there is an electrophilic and nncleophilic component. Therefore, the inclusion of electrophilic indole ring syntheses in this ch ter can be viewed as somewhat arbitrary, as was the case in Chapter 21 (Miscellaneons Nncleophilic Cyclizations). 

The classic Vilsmeier reagent is featured in two indole syntheses. Meth-Cohn and colleagues converted 

Indole Ring Synthesis From Natural Products to Drug Discovery, First Edition. Ga-don W. Gribble. 2016 John WQey Sons, Ltd. Published 2016 by John Wiley Sons, Ltd. 

We have already encountered some reduction methods en route to indole ring construction. Several classical indole name reactions feature reduction as the crucial step in indolization, and these are covered now. 

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Miscellaneous Reactions.—a-Alkoxylated a-lithioacetates may be alkylated,may react with ketones (the products from which cyclize to f3-lactones, themselves precursors of enol ethers by CO2 elimination" ), and may be condensed with lactones, as applied in a synthesis of natural product derivatives.The trianion derived from PhCH(0H)C02H is. C-alkylated but only in mediocre yield.The anions PhSCHCO and PhSCHC02Me react efficiently with electrophiles however, the former adds 1,2 to a, 8-unsaturated ketones, whereas the latter adds 1,4- ... 

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