A new general synthetic approach to diterpenes: application to syntheses of (.+-.)-taxodione and (.+-.)-royleanone

Enantioselective Synthesis of (+)-Royleanone from Sulfinyl Quinones

“…With MeOH (12 kbar) as solvent, 1,4-dihydroxy-2-isopropyl-3,6-dimethoxy-5-(p-tolylsulfinyl)benzene (5) was formed, and working in the presence of ZnBr 2 (CH 2 Cl 2 , 12 kbar) led to a complex reaction mixture, which contained, among other products, a benzofuran derivative 6, which has not been fully characterized. A similar structure resulting from an initial Michael-type addition of the vinyl moiety of 2 to C-6 of a benzoquinone derivative, followed by enolization of the intermediate and further cyclicization had been already reported by Engler et al [11] In accordance with our previous results, [12,13] the diastereoselectivity of Diels ± Alder reactions with 2-p-tolylsulfinyl quinone 4 a must be explained on steric grounds under the assumption that the major reaction involves a conformation of the sulfinyl quinone in which the sulfinyl oxygen atom is placed s-cis with respect to the dienophilic double bond (see Scheme 2). The favored approach of the diene from the face Scheme 2. bearing the lone pair of electrons at sulfur explains the formation of (S)-3 a as the major product.…”

“…[10] One of the more convergent approaches reported up to date relies on a Diels ± Alder reaction between an adequately substituted benzoquinone and 1,3,3-trimethyl-2-vinylcyclohexene as a key step. [11] In connection with our research devoted to asymmetric Diels ± Alder reactions with enantiomerically pure sulfinyl quinones, [12] we focused on these diterpenoid quinones bearing the angularly fused tricyclic skeleton with the aim of finding a general approach to efficiently create the C-10 asymmetric center. The protocol takes advantage of the tandem Diels ± Alder reaction/pyrolytic sulfoxide elimination which occurs when such sulfinyl quinones are allowed to react as dienophiles with acyclic dienes, and has been already applied to the efficient construction of other polycyclic quinones.…”

Effect of Abietane Diterpenes fromPlectranthus grandidentatuson the Growth of Human Cancer Cell Lines

“…Several abietane diterpenes of the royleanone and coleon type have been described as antimicrobial [1], [2], [3], antifungal [1], [2], [4], and antitumoral [4], [5] active metabolites. In the past we reported the antimicrobial activity of several royleanones isolated from Plectranthus hereroensis [1] and P. grandidentatus [2].…”

Diels-Alder Reactions of 12-Hydroxy-9(10®20)-5aH-abeo-abieta-1(10),8(9),12(13)-triene-11,14-dione

“…Quinones are excellent dienophiles for Diels-Alder reactions [48,49]. Nevertheless, the Diels-Alder reaction between quinone (S)-2 and any diene presents four fundamental questions that must be answered:…”