ChemInform Abstract: A Stereocontrolled Approach for the Synthesis of 2,5-Diaryl-3,4-disubstituted Furano Lignans Through a Highly Diastereoselective Aldol Condensation of an Ester Enolate with an α-Chiral Center: Total Syntheses of (-)-Talaumidin and (-)-Virgatusin.

ChemInform ◽  
2008 ◽  
Vol 39 (35) ◽  
Author(s):  
Kiran Matcha ◽  
Subrata Ghosh
Author(s):  
Rintaro Matsuo ◽  
Ayumu Watanabe ◽  
Shogo Kamo ◽  
Akinobu Matsuzawa ◽  
Kazuyuki Sugita

Concise total syntheses of penicibilaenes A and B were achieved via intramolecular aldol condensation and other key reactions.


1992 ◽  
Vol 70 (4) ◽  
pp. 1204-1220 ◽  
Author(s):  
Edward Piers ◽  
Richard W. Friesen

Alkylation of the substituted cycloalkanones 14a–d and 30 with (Z)-1-bromo-4-methyl-3-trimethylstannyl-2-pentene (13) produced compounds 15a–d and 33, which were readily converted into the corresponding enol trifluoromethane-sulfonates (triflates) 16a–d and 34. Intramolecular Pd(O)-catalyzed coupling of the vinylstannane and enol triflate functions in 16a–d and 34 provided the dienes 17a–d and 35. The annulation product 35 served as a suitable starting material for the total syntheses of the dolastane diterpenoids (±)-(5S,12R,14S)-dolasta-1(15),7,9-trien-14-ol (2) and (±)-amijitrienol (3). The key steps of the synthesis of (±)-2 involved the stereoselective methylation of the ketone 44 (readily derived from 35) to provide 46 and the Barbier type ring closure of 47 to provide the target compound. For the synthesis of (±)-3, the notable conversions included the reductive transformation of the diene 35 into the alkene 53, the aldol condensation of the ketone 54 with 4-trimethylstannyl-4-pentenal (55), the chemo- and stereoselective reduction of the dione 58, and the one-pot conversion of the keto vinylstannane 63 into the triene 65, via the intermediate 64.


1979 ◽  
Vol 57 (11) ◽  
pp. 1397-1398 ◽  
Author(s):  
Andrzej Robert Daniewski ◽  
Peter S. White ◽  
Zdenek Valenta

The title compound 8, a potential intermediate in the total synthesis of cardiac-active principles and other polyfunctional steroids, is prepared in nine steps using methyl vinyl ketone and 2-methylcyclohexane-1,3-dione as starting materials and acetylene and 2-methylcyclopentane-1,3-dione as additional sources of carbon atoms. In a crucial aldol condensation leading to the closure of steroid ring C, an efficient asymmetric induction by one chiral center leads to the establishment of three new chiral centers.


Author(s):  
Douglass F. Taber

The tetranortriterpenoid (–)-khayasin 3 recently emerged as a potent and selective insecticide against the Coconut leaf beetle Brontispa longissima. In considering a synthetic route to 3, Craig M. Williams of the University of Queensland envisioned (J. Org. Chem. 2012, 77, 8913) the convergent preparation of the allyl vinyl ether 1 and subsequent Claisen rearrangement to the enone 2. To pursue this strategy, the ketone 8 and the allylic alcohol 15 had to be prepared in enantiomerically pure form. To this end, the DIP-Cl-derived enolate of the ketone 7 was added to the aldehyde 6 to give a secondary alcohol, exposure of which to KH led to the enone 8 in high ee. Methyl triflate converted the enone into the enol ether 9. The α-pinene used in the preparation of DIP-Cl was 83% ee. The authors have optimized (Adv. Synth. Catal. 2009, 351, 1148) the Morita-Baylis-Hillman addition of cyclohexenone 10 to formaldehyde to give, after silylation, the enone 11. Methylation followed by DIP-mediated aldol condensation with 13 led to the alcohol 14. Exposure of the derived acetate to lithium diisopropylamide induced cyclization and dehydration. Deprotection completed the preparation (Tetrahedron 2006, 62, 7355) of 15. Fortunately, the enantiomers of 15 could be separated chromatographically. Material having >99% ee was taken onto the next step. Warming of 9 and 15 in the presence of acid delivered the coupled ketone 2 accompanied by the ether 1. Further heating of 1 converted it (Chem. Commun. 2011, 47, 2258) to 2. To form the last ring, the enone 2 was epoxidized to give 16. The reduction of 16 with aluminum amalgam gave preparatively useful amounts of 17. Esterification completed the synthesis of 3. Most total syntheses yield only the target natural product. In this biomimetic project, intermediates 15, 2, and 17 were themselves natural products, and oxidation of 17 delivered an additional natural product, 18. The preparation of 14 and of 8 underscores the importance of the asymmetric transformation of prochiral starting materials, cyclic and acyclic. Although DIP-Cl is used in stoichiometric amounts in both cases, it is not expensive. The preparation of 8, in particular, offers a potentially general approach to high ee-substituted cyclohexenones.


Author(s):  
B. J. Grenon ◽  
A. J. Tousimis

Ever since the introduction of glutaraldehyde as a fixative in electron microscopy of biological specimens, the identification of impurities and consequently their effects on biologic ultrastructure have been under investigation. Several reports postulate that the impurities of glutaraldehyde, used as a fixative, are glutaric acid, glutaraldehyde polymer, acrolein and glutaraldoxime.Analysis of commercially available biological or technical grade glutaraldehyde revealed two major impurity components, none of which has been reported. The first compound is a colorless, water-soluble liquid with a boiling point of 42°C at 16 mm. Utilizing Nuclear Magnetic Resonance (NMR) spectroscopic analysis, this compound has been identified to be — dihydro-2-ethoxy 2H-pyran. This impurity component of the glutaraldehyde biological or technical grades has an UV absorption peak at 235nm. The second compound is a white amorphous solid which is insoluble in water and has a melting point of 80-82°C. Initial chemical analysis indicates that this compound is an aldol condensation product(s) of glutaraldehyde.


2013 ◽  
Vol 17 (19) ◽  
pp. 2192-2224 ◽  
Author(s):  
Majid Heravi ◽  
Elaheh Hashemi ◽  
Nazanin Ghobadi

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