Chemistry and kinetics of α- and β-naphthyl(phosphonyl)carbenes. Effects of positions on neighbouring phosphonate participation

Abstract

A series of naphthyldiazomethanes 1 having either (dimethyl)phosphonyl [a: (MeO)₂P(O)–] or sodium (monomethyl)phosphonate [b: (MeO)(NaO)P(O)–] groups at positions α or β have been prepared and the effects of these substituents on the naphthylcarbenes (2) generated by photolysis of the corresponding diazo compounds have been investigated both by product analysis and by spectroscopic means.

A marked difference in the reaction patterns and reactivities between the α- and β-isomers of 2a can be explained in terms of differences in electrophilicity of the carbenic centre due to the naphthyl moiety HOMO and of the interaction between the carbene centre and the peri-hydrogen. On the other hand, the dramatic increase in the reactivity towards the OH bond relative to the alkenic double bond of the phosphonate anion indicates that the neighbouring phosphonate group must interact with the vacant p-orbital of a singlet carbene and thus reduce the electrophilicity of the carbene.