Allylating

Allylating refers to the introduction of an allyl group (three-carbon allyl group, CH2=CH-CH2-) into a substrate, forming a new carbon–carbon or carbon–heteroatom bond. Allylation is a common strategy in organic synthesis for constructing homoallylic frameworks and for installing allyl functionality that can be transformed further.

Reagents include allyl halides (e.g., allyl chloride), allyl esters or carbonates, and allyl silanes, as well as organometallic reagents such as allyl lithium, allylmagnesium bromide, and catalytic systems that generate π-allyl metal intermediates.

Two broad modalities are distinguished: carbon-allylation, in which the allyl group is installed to form C–C bonds, and heteroatom allylation (N-, O-, S-allylation), which attaches the allyl group to nitrogen, oxygen, or sulfur. A central, widely used method for C–allylation is the Tsuji–Trost reaction, where a nucleophile adds to a π-allyl–metal complex (often palladium) generated from an allyl electrophile and a leaving group. This pathway enables formation of homoallylic products with high regio- and stereocontrol in many cases. SN2′ processes (allyl substitutions at the terminal carbon of the allyl system) also contribute to C–allylation with various catalysts and reagents.

N-allylation and O-allylation are common, typically using allyl halides or carbonate reagents, and can be catalyzed to achieve selectivity. Allylation is widely used to assemble complex molecules, including natural products, by installing an allyl handle that can be converted to alcohols, alkenes, or other functionalities.