Pyridine reaction with singlet carbene

Because of the presence of a lone pair and a vacant orbital, singlet carbenes are supposed to be able to react with both Lewis bases and acids. Transient electrophilic carbenes are known to react with Lewis bases to give normal ylides (Scheme 8.19). For example, carbene-pyridine adducts have been spectroscopically characterized and used as a proof for the formation of carbenes,and the reaction of transient dihalogenocarbenes with phosphines is even a preparative method for C-dihalogeno phosphorus ylides. Little is known about the reactivity of transient carbenes with Lewis acids. 

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