Regio-Controlled Michaelis-Arbuzov Reactions of 3-(halomethyl)-coumarins

3-(Iodomethyl)coumarins and 3-(chloromethyl)coumarins, obtained chemoselectively via Baylis–Hillman reactions of salicylaldehyde derivatives with t-butyl acrylate, can be reacted with triethyl phosphite to afford regioisomeric Michaelis-Arbuzov products. Under nitrogen, the 3-(iodomethyl)coumarins undergo direct displacement of iodide to afford the expected 1′-phosphonated derivatives. The reactions with 3-(chloromethyl)coumarins in air, however, proceed with overall allylic rearrangement to afford the regioisomeric 3-methyl-4-phosphonated derivatives.