Naturally occurring enantiomers of three diterpenes isolated as phytoalexins from rice blast leaves were synthesized:(+)-oryzalexin. A [ent-3β-hydroxyisopimara-8 (14), 15-dien-7-one, 1],(+)-oryzalexin B [ent-7α-hydroxyisopimara-8 (14), 15-dien-3-one, 2] and (+)-oryzalexin C [ent-isopimara-8 (14), 15-diene-3, 7-dione, 3]. Their antipodes were also synthesized.