Abstract Optically active A-factor (1), the factor from Streptomyces viridochromogenes (2), the factors from S. bikiniensis and S. cyaneofuscatus (3–5), and virginiae butanolides A (6), B (7), C (8), and D (9) were synthesized starting from (S)-(−)-paraconic acid (10). The absolute configurations of virginiae butanolides A and C were deduced to be (2S, 3R, 1′ R).