Spongian pentacyclic diterpenes. Stereoselective synthesis of (-)-dendrillol-1

Photochemische Reaktionen als Schlüsselschritte in der Naturstoffsynthese

“…In der Synthese von (À)-Dendrillol-1 (296) wurde vom Photocycloadditionsprodukt 294 des Enons 293 mit Acetylen T. Bach und J. P. Hehn Aufsätze Gebrauch gemacht, das diastereoselektiv gebildet wird (Schema 77). [373] Die Spaltung der Doppelbindung erfolgte am Ende der Synthese durch Ozonolyse, sodass die Carbonsäure 295 direkt in das Zielmolekül überführt wurde.…”

Complete assignment of the 1H NMR data and reassignment of 13C NMR data of four spongian diterpenes

“…Dendrillol‐1 ( 2 ), ‐2 ( 3 ), and aplyroseol‐6 ( 4 ) possess the same pentacyclic ring skeleton and differ from each other in the level of oxidation and esterification in Ring B. Three previous publications have reported NMR spectroscopic data for dendrillol‐1 ( 2 ) . Inspection of 2D NMR data has allowed us to reassign the chemical shift for one proton (H‐11α; previously assigned as H‐9), to define the chemical shifts for all of the prochiral methylene protons in Ring A, to assign the chemical shifts for the four protons (H‐1α, H‐2α, H‐2β, and H‐3β) that were previously unassigned, and to report the 1 J CH coupling constants at 15 positions (Table ).…”

“…Three previous publications have reported NMR spectroscopic data for dendrillol-1 (2). [5,9,10] Inspection of 2D NMR data has allowed us to reassign the chemical shift for one proton (H-11α; previously assigned as H-9), to define the chemical shifts for all of the prochiral methylene protons in Ring A, to assign the chemical shifts for the four protons (H-1α, H-2α, H-2β, and H-3β) that were previously unassigned, and to report the 1 J CH coupling constants at 15 positions ( Table 2). The proton signal at δ H 1.64 was assigned to H-11α by Ksebati and Schmitz in 1992.…”

Photo-Oxidation of Aldehydes with Molecular Oxygen in the Presence of Catalytic Bromine or Hydrobromic Acid

“…3-7) Herein, we report in detail our study on the generality and limitation of this aerobic photo-oxidation of aldehydes to the carboxylic acids [10][11][12][13][14][15][16][17][18][19][20][21][22] in the presence of a catalytic bromine or hydrobromic acid, which are inexpensive, safe and easily separable from the reaction mixture by extraction. Table 1 shows the results of a study of reaction conditions conducted with 1 as test substrate and catalytic bromine as promoter under irradiation with a 400 W high-pressure mercury lamp externally in an oxygen atmosphere.…”