Fortschritte der Chemie organischer Naturstoffe / Progress in the Chemistry of Organic Natural Products
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1. Structure and Occurrence Aromadendranes (1) belong to a class of sesquiterpenes, structurally characterized by a dimethyl cyclopropane ring fused to a hydroazulene skeleton, as depicted in Fig. 1. Throughout this and the following sections the numbering of the carbon skeleton will be used as given in (1). Next to the aromadendranes, the related sesquiterpenes with a 1,7-cycloaromadendrane, 7,8-seco-, and 9,lO-secoaromadendrane skeleton will be discussed. Some dimeric and alkylated aromadendranes, e.g. macrocarpals and prenylaromadendranes are also included in this review. The literature is covered through September 1993. The name "aromadendrane" originates from the sesquiterpene ( + )aromadendrene (2), the first reported sesquiterpene with this skeleton (1).
%iH Fig. 1. The aromadendrane skeleton and numbering
J. B. Barrera et al., Fortschritte der Chemie organischer Naturstoffe / Progress in the Chemistry of Organic Natural Products © Springer-Verlag/Wien 1995
150
H.1. M.
GIJSEN,
(+ )-Aromadendrene is a
J. B. P.
A. WIJNBERG,
and
AE. DE GROOT
constituent of the essential oil extracted from the wood of Eucalyptus trees. In earlier days the trees belonging to this genus were known as Aromadendron trees. After numerous experiments, the structure of ( + )-aromadendrene (2) was elucidated in 1953 (2), but it took thirteen years before BOeHl et al. in 1966 established the absolute configuration of2 through the synthesis of (- )-aromadendrene starting from (- )-perillaldehyde (3) (see Sect. 4). In addition, the absolute configurations of alloaromadendrene (3), in which the hydroazulene skeleton is cis-fused, and the related tertiary C7alcohols globulol (4), epiglobulol (5), ledol (6), and viridiflorol (7) were established. Gurjun balsam, the resin from tropical trees belonging to the Diptero~ carpaceae family, provided the aromadendrane ( - )-cx-gurjunene (25) (4), whose structure was determined in 1963 by OURISSON et al. (5). This hydrocarbon can be oxidized to the cx,~-unsaturated ketone ( - )-cydocolorenone (27) (6), which has been isolated from Pseudowintera colorata (7). The stereochemistry of (27) was independently determined through synthesis of its C8-epimer in 1966 (8). All the compounds mentioned so far are present in numerous plant species. Other frequently occurring aromadendranes are the tertiary C8 and Cll alcohols palustrol (8) and spathulenol (31), respectively, and the hydrocarbon ledene (43), also known as viridiflorene (9). A number of other aromadendrane hydrocarbons have been isolated from the oil or resin obtained from different tree species. Gurjun balsam contains besides cx-gurjunene (25) also its C7 epimer (26) (10). Tolu balsam, obtained from Myroxylon balsamum var. balsamum, was found to contain the five hydrocarbons (52), (53), (54), (55), and (56) (11). The aromadendrane hydrocarbon ~-spathulene (51) is a minor component in the oil of Schinus Molle (12). In many aromadendranes C7 and/or Cll are oxidized. Although less frequently, oxidation at all the oth
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