Diterpenoide Drüsenfarbstoffe aus Labiaten: 3β‐Acetoxyfuerstion, Nilgherron A und Nilgherron B, neue Chinomethane aus Plectranthus nilgherricus B ENTH .; absolute Konfiguration von Fuerstion

Leaf‐gland Pigments: 3β‐Acetoxyfuerstione, Nilgherron A and Nilgherron B, New Quinomethanes from Plectranthus nilgherricus BENTH. (Labiatae); Absolute Configuration of Fuerstione We have isolated from leaf‐glands of the above mentioned plant the following deeply coloured quino‐methane derivatives: (1) traces of the already known fuerstione (1a); 11,15‐dihydroxy‐5,7,9 (11), 13‐abietatetraen‐12‐one; (2) the new 3β‐acetoxy‐fuerstione (1b); (3) nilgherron A (5a, I or II), a new dimeric diterpenoid quinomethane, C40H52O7, formed in the plant obviously by cycloaddition of the o‐quinone 8 (9aS, 11R)‐11 ‐hydroxy‐2‐(1‐hydroxy‐1‐methylethyl‐9,9‐dimethyl‐3,4,7,8,9,9a,10,11‐ octahydro‐5H‐dibenzo [a, d]cycloheptene‐3,4‐dione) with fuerstione; (4) nilgherron B (5b, I or II), C42H54O9, likewise a new compound, formed by the same type of cycloaddition (heterodiene synthesis) of 8 with 3β‐acetoxyfuerstione. On the basis of 1H‐NMR. shift arguments structure I is slightly preferred to II for 5a and 5b. Model experiments have shown the easy formation of the dihydrodioxin ring by reaction of an o‐benzoquinone with p‐quinomethanes. The absolute configuration of fuerstione and 3β‐acetoxyfuerstione has been determined by chiroptical methods.