Synthesis of (±)-Chokol A by a Tandem Michael-Addition/Dieckmann Cyclization
1994, Groth, Ulrich, Halfbrodt, Wolfgang, Köhler, Thomas, Kreye, Paul
A total synthesis of (±)-chokol A (rac-12) was accomplished in five steps by starting from the α,β-unsaturated ester (E)-2 in an overall yield of 24%. The key step of this synthesis is the tandem conjugate addition/Dieckmann cyclization of the cuprate derived from vinyl bromide 9 with the α,β-unsaturated ester (E)-2.
Addition of Cerium Reagents Derived from (Trimethylsilyl)propargyl Bromide to Aldehydes
1994, Eckenberg, Peter, Groth, Ulrich, Köhler, Thomas
The addition of (trimethylsilyl)propargylmagnesium bromide (9) to aldehydes afforded predominantly the allenylic alcohols rac-10. The regioselectivity of this addition changes dramatically when organocerium reagents were used for the addition. In this case nearly exclusive formation of the homopropargylic alcohols rac-8 was observed. Highest selectivity for this process was obtained when cerium(III) isopropoxide (13) was used as a precursor for the formation of the organocerium reagent.
Asymmetric Synthesis via Heterocyclic Intermediates, LII. Synthesis of tert-Leucine and Related Amino Acids
1993, Groth, Ulrich, Huhn, Thomas, Porsch, Bettina, Schmeck, Carsten, Schöllkopf, Ulrich
The 2,5-dialkoxypyrazines 3a and b were prepared in three steps from methyl glycinate hydrochloride (1) in an overall yield of 18 and 63%. Upon the addition of lithium organyls to 3b and subsequent acidic hydrolysis the ethyl glycinates rac-7 were obtained.
rac-1,1,4-Trimethyl-5-trimethylsilyl-1,3,3a,4,6,7,8,9-octahydro-1-silanaphtho[1,2-c]furan at 153 K
1995, Pohl, Ehmke, Herbst-Irmer, Regine, Groth, Ulrich, Eckenberg, Peter
The crystal structure of rac-1,1,4-trimethyl-5-trimethylsilyl-1,3,3a,4,6,7,8,9-octahydro-1-silanaphtho[1,2-c]-furan, C17H30OSi2, has been determined at low temperature.
Alpha-Alkylidenecyclopentanones by Alpha-Alkylidation of Methyl 2-Oxocyclopentanecarboxylate
1994, Arnecke, Ralf, Groth, Ulrich, Köhler, Thomas
An α-alkylidation of cyclopentanone was achieved in two reaction steps in an overall yield of 20 to 79% via a zinc chloride-catalyzed thioalkylation of the zinc enolate of methyl 2-oxocyclopentanecarboxylate (3) and subsequent saponification/desulfurization of the β-(phenylthio) ketone intermediates 5. For the saponificatioddesuiurization step DABCO proved to be the reagent of choice and superior to the use of alkali or magnesium halides.
Synthesis of Enantiomerically Pure Hexahydro-1H-indenes and Substituted Cyclopentanes as Intermediates for the Synthesis of Steroids
1994, Groth, Ulrich, Taapken, Thomas
The indene derivative 7 and the 1,2,2,3-tetrasubstituted cyclopentane derivative 8 have been synthesized in three steps starting from the Hajos-Wiechert ketone 1.
A Diaza-cyclo-tetradecadiene-Bis(pyrido-silafuran) Ring System
1995, Pohl, Emke, Herbst-Irmer, Regine, Huhn, Thomas, Groth, Ulrich
The crystal structure of 8,8,20,20-tetramethyl-9,21-dioxa-25,26-diaza-8,20-disilapentacyclo[18.104.22.168,13.07,11.019,23]_ hexacosa-1(25),6,11,13(26),18,23-hexaene, C24H34N2O2-Si2, has been determined at low temperature. The molecule lies on a crystallographic inversion centre.
Alpha-Thioalkylation of Zinc Dienolates to 4-Substituted 1-tert-Butoxy-7a-methyl-hexahydroinden-5-ones
1994, Groth, Ulrich, Köhler, Thomas, Taapken, Thomas
α-Alkylation of the α,β-unsaturated ketone 1 at C-4 has been achieved by thioalkylation of the corresponding zinc dienolate with α-chlorosulfides of type 2. The desulfurization of the β-(phenylthio) ketones 4 leads directly to the 4-substituted hexahydroinden-5-ones 5.
Di-My-chloro-bis[dichlorotris(2-propanol)cerium(III)] at 153 K
1994, Schäfer, Martina, Herbst-Irmer, Regine, Groth, Ulrich, Köhler, Thomas
The structure of di-μ-chloro-bis[dichlorotris(2-propanol)cerium(III)], [CeCl3(C3H80)3]2, is reported. The Ce atoms are bridged by two C1 atoms and so a dimer is formed.