Treatment of methyl mesopyropheophorbide a with formaldehyde under basic conditions gave a novel 13(2)-methylene derivative in 85% yield; under acidic conditions, the corresponding 20-hydroxymethyl derivative was obtained in 65% yield. The high reactivity of the enone structural motif existed in the former product provides a unique way to construct some novel chlorophyll a derivatives for various applications. Stereoselective Michael reaction of this compound is studied and discussed.