 For addition of sulfur ylides to enones , higher 1 @,@ 4 @-@ selectivity is typically obtained with sulfoxonium reagents than with sulfonium reagents . Many electron @-@ withdrawing groups have been shown compatible with the reaction including ketones , esters , and amides ( the example below involves a Weinreb amide ) . With further conjugated systems 1 @,@ 6 @-@ addition tends to predominate over 1 @,@ 4 @-@ addition . 
 For addition of sulfur ylides to enones , higher 1 @,@ 4 @-@ selectivity is typically obtained with sulfoxonium reagents than with sulfonium reagents . Many electron @-@ withdrawing groups <a href='been_done' title='1'><mark>have</mark></a> been shown compatible with the reaction including ketones , esters , and amides ( the example below <a href='uninflect' title='2'><mark>involves</mark></a> a Weinreb amide ) . With further conjugated systems 1 @,@ 6 @-@ addition <a href='uninflect' title='3'><mark>tends</mark></a> to predominate over 1 @,@ 4 @-@ addition . 
For addition of sulfur ylides to enones , higher 1 @,@ 4 @-@ selectivity is typically obtained witt sulfoxonium reagents than with sulfonium reagents . Many electron @-@ withdrawing groups done been shown compatible with da reaction including ketones , esters , and amides ( the example below involve a Weinreb amide ) . With further conjugated systems 1 @,@ 6 @-@ addition tend to predominate ova 1 @,@ 4 @-@ addition .