Ein neuer synthetischer Zugang zu Ubichinonen

A New Synthetic Route to Ubiquinones Ubiquinones 11 have been prepared employing a new strategy: as key step, the Diels-Alder reaction of 1,1,2-trichloroethene 3 with 2,5-bis[(trimethylsilyl)oxy]-3-methylfuran ( 2 ) has been used for the construction of the quinone part. After methanolysis of the [4 + 2] adducts 4a/4b , further reaction with cyclopentadiene and substitution of the Cl-atoms by MeO groups, the intermediate 7 is obtained. Diketone 7 can easily be alkylated with the desired polyprenyl side chain 9 (X = Br) using a strong base to yield, after a retro-Diels-Alder reaction, the corresponding ubiquinones 11 in high yields.     

Ein neuer Zugang zu halogenierten Carboranen

The copyrolysis of tetrahalogenodiborane(4) (B₂X₄, X = Cl, Br) or the halogenated carbon compounds such as CX₄ or C₂X₄ yields the new carboranes C₂B₅X₇ and C₂B₇Cl₉ in addition to the vinyl compound C₂Br₃BBr₂ as some of the products.     

Photolactonisierung: Ein neuer synthetischer Zugang zu Makroliden

Photolactonization: A Novel Synthetic Entry to Macrolides o-Quinol acetates, hydroxyalkylated at C(6), are easily accessible from simple phenols by Wessely acetoxylation (preferentially catalyzed by BF₃). On UV irradiation (in the presence of an appropriate tertiary amine), they are smoothly converted to macrocyclic lactones. Subtle conditions have been elaborated to lead to high overall yields, and the scope of the conversion of phenols to macrolides has been elucidated.     

Ein neuer Zugang zu Bicyclo[4.1.0]heptan-Derivaten

A New Approach to Bicyclo[4.1.0]heptane Derivatives The reaction of the dienone 1 with ethyl α-bromoacetate does not furnish the expected glycidic acid ester 2 but leads to the bicyclo[4.1.0]heptenone derivative 3 . The structure of this new compound has been proved by means of spectroscopic methods (1R, ¹H-NMR, ¹³C-NMR, MS). The elucidation of the configuration at C(7) could be realized by measuring a NOE effect. Other α-alkylated α-bromoacetates react with 1 in the same manner.     

Ein neuer Zugang zu 2,6,6-Trimethylcyclohexa-2,4-dienon aus 4-Oxoisophoron

A New Access to 2,6,6-Trimethylcyclohexa-2,4-dienone from 4-Oxoisophorone 2,6,6-Trimethylcyclohexa-2,4-dienone ( 1 ), a versatile starting material for the preparation of some carotenoids and several natural products, was efficiently (73% yield) prepared from oxoisophorone 3 . After conversion of 3 to the alcohol 4 or the acetate 5 , H₂O was eliminated ( 4→1 ) under acidic distillative conditions, whereas AcOH could be eliminated ( 5→l ) under Pd(O) catalysis.