331233-81-9Relevant academic research and scientific papers
Asymmetric Synthesis of Hispidanin A and Related Diterpenoids
Cao, Wei,Deng, Heping,Sun, Ying,Liu, Bo,Qin, Song
, p. 9120 - 9129 (2018)
We report on our accomplishment of the asymmetric synthesis of hispidanin A and its natural precursor, a labdane diterpenoid. In the first generation of synthesis, a semi-synthesis strategy was employed to construct a labdane-type diterpenoid, a natural precursor of hispidanin A, in which Barton's photolytic remote functionalization was employed as a key transformation. In addition, the totarane-type dienophile counterpart was derived from commercially available (?)-scalareol. In the second generation of synthesis, key elements included an iron-catalyzed radical cascade to access the labdane-type diene on the basis of hydrogen atom transfer, and an enantioselective cationic polyene cyclization furnished the totarane-type dienophile. Reaction optimization and mechanistic analysis of the radical cascade reaction was conducted. Furthermore, the [4+2] cycloaddition reaction was achieved in excellent yield and selectivity under thermal conditions, which has been rationalized by using DFT transition-state analysis and paved the way for final accomplishment of the total synthesis of hispidanin A.
Asymmetric Total Synthesis of Hispidanin A
Deng, Heping,Cao, Wei,Liu, Rong,Zhang, Yanhui,Liu, Bo
, p. 5849 - 5852 (2017)
Asymmetric total synthesis of the dimeric diterpenoid hispidanin A was accomplished by non-catalytic Diels–Alder cycloaddition at room temperature. The synthesis relies on iron-catalyzed coupling to construct a Z-configured trisubstituted alkene, an iron-catalyzed radical cascade to generate a labdane-type diene, and both Yamamoto cationic polyene cyclization and palladium-catalyzed Stille coupling to generate a totarane-type dienophile.
Enantio- and diastereoselective stepwise cyclization of polyprenoids induced by chiral and achiral LBAs. A new entry to (-)-ambrox, (+)-podocarpa-8,11,13-triene diterpenoids, and (-)-tetracyclic polyprenoid of sedimentary origin
Ishihara, Kazuaki,Ishibashi, Hideaki,Yamamoto, Hisashi
, p. 3647 - 3655 (2007/10/03)
An enantio- and diastereoselective stepwise cyclization of polyprenoids induced by Lewis acid-assisted chiral Bronsted acids (chiral LBAs) and achiral LBAs is described. In particular, the absolute stereocontrol in the initial cyclization of polyprenoids to form an A-ring induced by chiral LBAs and the importance of the nucleophilicity of the internal terminator in polyprenoids for the relative stereocontrol in subsequent cyclization are demonstrated. (-)-Ambrox was synthesized via the enantioselective cyclization of (E,E)-homofarnesyl triethyrsily ether with triethylsilyl ether with tin(IV) chloride-coordinated (R)-2-(o-fluorobenzyloxy)-2′-hydroxy-1,1′-binaphthyl ((R)-BINOL-o-FBn) and subsequent diastereoselective cyclization with CF3CO2H·SnCl4 as key steps. Protection of (E,E)-homofarnesol by a triethylsilyl group increased the enantioselectivity of chiral LBA-induced cyclization and both the chemical yield and diastereoselectivity in the subsequent cyclization. The enantioselective cyclization of homo(polyprenyl)arenes possessing an aryl group was also induced by (R)-BINOL-o-FBn·SnCl4. Several optically active podocarpa-8,11,13-triene diterpenoids and (-)-tetracyclic polyprenoid of sedimentary origin were synthesized (75-80% ee) by the enantioselective cyclization of homo(polyprenyl)benzene derivatives induced by (R)-BINOL-o-FBn·SnCl4 and subsequent diastereoselective cyclization induced by BF3-Et2O/EtNO2 or CF3CO2H·SnCl4.
