An Expeditious Synthesis of Methyl Jasmonate

We present an efficient three‐step, two‐pot synthesis of methyl jasmonate (trans‐1) based on Diels–Alder cycloaddition of cyclopent‐2‐enone (2) and chloroprene (= 2‐chlorobuta‐1,3‐diene; 3d) in either CHCl3 or CH2Cl2, catalyzed by SnCl4 (0.2 mol‐equiv.) at 20° (75% yield). Subsequent ozonolysis of a cis/trans 55 : 45 mixture of the cycloadduct 4d in either CH2Cl2 or AcOEt at − 78°, followed by addition of Me2S and MeOH in the presence of NaHCO3, afforded, in 64% yield, a cis/trans 40 : 60 mixture of the known aldehyde 5c. The latter was reacted at − 50° under salt‐free conditions with the propyl Wittig reactant to furnish 1 as a cis/trans 20 : 80 mixture ((E/Z) 3 : 97). Alternatively, a cis/trans 7 : 93 mixture ((E/Z) 4 : 96) was obtained in 88% yield from epimerized 5c (AcOH, H2O, 40°; 99%) under usual Wittig conditions at − 20°.