Synthesis of 4-(21-nor-5-pregnen-20-yl)-1,3-thiazole derivatives

1984 ◽  
Vol 49 (4) ◽  
pp. 1051-1059 ◽  
Author(s):  
Pavel Drašar ◽  
Vladimír Pouzar ◽  
Ivan Černý ◽  
Miroslav Havel
Keyword(s):  
Osmium Tetroxide ◽  
Hydroxy Ketone ◽  
Hantzsch Reaction ◽  
Enol Ether ◽  
Thiazole Derivatives ◽  
Silyl Enol Ether

The keto sulfoxide IV, prepared from the ester III, was reduced with amalgamated aluminium to give the ketone V which after enolization and silylation afforded the silyl enol ether VI. Oxidation of VI with osmium tetroxide and N-methylmorpholine N-oxide monohydrate yielded the α-hydroxy ketone VII. This was converted into the mesylate IX and further into the bromo ketone XI which on Hantzsch reaction with ethyl thioxamate furnished the steroidal thiazole XII. Compound XII was converted into the hemisuccinate XIV.

Synthesis of 17β-[4-(1,3-thiazolyl)]androstane 3β-hemisuccinate and glycoside

1984 ◽  
Vol 49 (4) ◽  
pp. 1039-1050 ◽  
Author(s):  
Pavel Drašar ◽  
Vladimír Pouzar ◽  
Ivan Černý ◽  
Jorga Smolíková ◽  
Miroslav Havel
Keyword(s):  
Osmium Tetroxide ◽  
Hydroxy Ketone ◽  
Hantzsch Reaction ◽  
Bromo Derivative

The protected 20(21)-en-20-ol ether III was oxidized with N-methylmorpholine N-oxide monohydrate and osmium tetroxide to give the hydroxy ketone IV which was converted into the bromo derivative VIII via the mesylate VI. Hantzsch reaction of the bromo ketone VIII with ethyl thioxamate afforded the thiazole XI whose hemisuccinate XIII and glycoside XV were prepared.

Organic Functional Group Transformation

2013 ◽  
Author(s):  
Douglass F. Taber
Keyword(s):  
Allylic Alcohol ◽  
Hydroxy Ketone ◽  
Enol Ether ◽  
Ru Catalyst ◽  
Boston University ◽  
Chlorosulfonyl Isocyanate ◽  
University Of Technology ◽  
Silyl Enol Ether ◽  
The University ◽  
Functional Group Transformation

Susumu Saito of Nagoya University developed (Angew. Chem. Int. Ed. 2011, 50, 3006) Fe-catalyzed conditions, compatible with alkenes, for converting an alcohol 1 to the amine 2. Corey R. J. Stephenson of Boston University took advantage (Nature Chem. 2011, 3, 140) of photoredox catalysis to convert an alcohol 3 to the iodide 4. Jing-Mei Huang of the South China University of Technology condensed (J. Org. Chem. 2011, 76, 3511) the halide 5 with benzaldehyde and aqueous ammonia to give the imine 6. Young Hoon Jung of Sungkyunkwan University used (Tetrahedron Lett. 2011, 52, 1901) chlorosulfonyl isocyanate to convert a benzylic (or allylic) ether 7 into the urethane 8. David Crich of Centre de Recherche de Gif coupled (Org. Lett. 2011, 13, 2256) the isocyanate 9 with the acid 10 to give the amide 11. Tobias Ritter of Harvard University effected (J. Am. Chem. Soc. 2011, 133, 1760) α-hydroxylation of the acidic ketone 12 by exposure to O2 in the presence of a Pd catalyst. Gowravaram Sabitha of the Indian Institute of Chemical Technology, Hyderabad, activated (Org. Lett. 2011, 13, 382) Pd(OH)2 by exposure to H2 , then used the activated catalyst to isomerize the allylic alcohol 14 to the aldehyde 15 . Richard C. Hartley of the University of Glasgow combined (Tetrahedron Lett. 2011, 52, 3020) commercial Nysted reagent and Cp2 TiCl2 to methyl-enate the ester 16. The enol ether 17 is a versatile intermediate, giving, inter alia, the methyl ketone by hydrolysis, or the α-hydroxy ketone on exposure to peracid. The activation of alkynes continues to be an area of vigorous investigation. Lukas Hintermann of the Technische Universitä t München devised (J. Am. Chem. Soc. 2011, 133, 8138) a Ru catalyst for the hydration of 18 to the aldehyde 19. Issa Yavari of Tarbiat Modares University effected (Tetrahedron Lett. 2011, 52, 668) oxidation of 20 to the N-sulfonyl amidine 22. Craig A. Merlic of UCLA coupled (Org. Lett. 2011, 13, 2778) 24 with the vinyl boronate derived from 23 to give the silyl enol ether 25. Li-Biao Han of AIST Tsukuba prepared (Chem. Commun. 2011, 47, 2333) 28 by adding 27 to 26.

The Nicolaou/Li Synthesis of Tubingensin A

2015 ◽  
Author(s):  
Douglass F. Taber
Keyword(s):  
Aldol Condensation ◽  
Physiological Activity ◽  
Secondary Alcohol ◽  
Hydroxyl Group ◽  
Hydroxy Ketone ◽  
Magnesium Bromide ◽  
Enol Ether ◽  
Quaternary Centers ◽  
Silyl Enol Ether ◽  
Aspergillus Sp

The complex indole diterpene alkaloids, isolated both from Aspergillus sp. and from Eupenicillium javanicum, display a wide range of physiological activity. K.C. Nicolaou of Scripps/La Jolla and Ang Li, now at the Shanghai Institute of Organic Chemistry, conceived (J. Am. Chem. Soc. 2012, 134, 8078) a divergent strategy for the assembly of these alkaloids that enabled syntheses of both anominine (not illustrated) and tubingensin A 3. A key step in the assembly of the carbocyclic skeleton of both alkaloids was the radical cyclization of 1 to 2, establishing the second of the two alkylated quaternary centers of 3. The starting point for the preparation of 1 was commercial pulegone 4. Methylation followed by acid-mediated retro aldol condensation delivered the enantiomerically pure 2,3-dimethyl cyclohexanone 5. To maximize yield, the subsequent Robinson annulation was carried out over three steps, formation of the silyl enol ether, condensation of the enol ether with methyl vinyl ketone 6, and base-mediated cyclization and dehydration of the 1,5-diketone to give 7. The secondary hydroxyl group was introduced by exposure to Oxone of the methyl dienol ether derived from 7. The mixture of diastereomers from the radical Ueno-Stork cyclization of 1 was equilibrated to the more stable 2 by exposure to acid. The authors took advantage of the regioselective enolization of 2, preparing the silyl enol ether, which could then be condensed with formaldehyde to give 10. This hydroxy ketone was carried onto 11 over four steps, commencing with silylation and proceeding through Wittig condensation, desilylation, and oxidation. The addition of the Grignard reagent 12 to the aldehyde 11 gave a secondary alcohol, which was readily dehydrated to the diene 13. The diene resisted thermal cyclization, but on exposure to CuOTf at room temperature it was smoothly cyclized and oxidized to 14. The elaboration of the sidechain had already been worked out in the anominine synthesis. The free lactol derived from 14 resisted many nucleophiles, but vinyl magnesium bromide did add. Bis acetylation of the resulting diol followed by Pd-mediated ionization and reduction of the allylic acetate, and reductive removal of the residual acetate, delivered the terminal alkene 15. Metathesis with isobutylene gave 16, which was deprotected to give tubingensin A 3.

Synthesis of α-Arylcarboxylic Acid Amides from Silyl Enol Ether via Migratory Amidation with 2-Azido-1,3-dimethylimidazolinium Hexafluorophosphate

2013 ◽  
Vol 42 (7) ◽  
pp. 691-693 ◽  
Author(s):  
Mitsuru Kitamura ◽  
Kento Murakami ◽  
Yuichiro Shiratake ◽  
Tatsuo Okauchi
Keyword(s):  
Enol Ether ◽  
Silyl Enol Ether

Carbon-carbon bond formation in reactions of PhIO.cntdot.HBF4-silyl enol ether adduct with alkenes or silyl enol ethers

1989 ◽  
Vol 54 (11) ◽  
pp. 2605-2608 ◽  
Author(s):  
V. V. Zhdankin ◽  
M. Mullikin ◽  
Rik Tykwinski ◽  
Bruce Berglund ◽  
Ronald Caple ◽  
...  
Keyword(s):  
Bond Formation ◽  
Enol Ether ◽  
Enol Ethers ◽  
Carbon Bond ◽  
Silyl Enol Ethers ◽  
Carbon Carbon Bond ◽  
Silyl Enol Ether

An Access to Highly Enantioenriched cis-3,5-Disubstituted γ-Lactones from α-Bromoacetate and Silyl Enol Ether

2021 ◽  
Author(s):  
Ha Rim Lee ◽  
Seo Yun Kim ◽  
Min Ji Park ◽  
Yong Sun Park
Keyword(s):  
Nucleophilic Substitution ◽  
Enol Ether ◽  
Enol Ethers ◽  
Silyl Enol Ethers ◽  
Synthetic Strategy ◽  
Silyl Enol Ether

A novel synthetic strategy for highly enantioenriched cis-3,5-disubstituted γ-lactones has been developed by the AgOTf-promoted nucleophilic substitution of α-bromoacetates with silyl enol ethers and subsequent reductive lactonization. The utility of...

Silyl Enol Ether Based Nucleophiles

2012 ◽  
pp. 1
Author(s):  
D. W. C. MacMillan ◽  
A. J. B. Watson
Keyword(s):  
Enol Ether ◽  
Silyl Enol Ether
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