Part 1: Efficient strategies for the construction of variably substituted bicyclo[5.3.1]undecenones (AB taxane ring systems)

2004 ◽  
Vol 82 (2) ◽  
pp. 215-226 ◽  
Author(s):  
Alain Laurent ◽  
Nidia P Villalva-Servín ◽  
Pat Forgione ◽  
Peter D Wilson ◽  
David V Smil ◽  
...  
Keyword(s):  
Lewis Acid ◽  
Boron Trifluoride ◽  
Boron Trifluoride Etherate ◽  
Diels Alder ◽  
Ring Systems ◽  
Electronic Nature ◽  
Single Diastereomer ◽  
Cyclic Molecules ◽  
The Cross ◽  
Propargyl Alcohols

Strategies for the construction of cyclic molecules containing variably substituted bicyclo[5.3.1]undecenones (AB taxane ring systems) are described. These routes employ a multi-component coupling protocol that utilizes sequential magnesium-mediated carbometallation of propargyl alcohols and intramolecular Diels–Alder reactions (IMDA). The cycloaddition generates the key eight-membered taxane ring as a single diastereomer, induced by preferential Lewis acid (diethylaluminum chloride or boron trifluoride etherate) complexation with the cross-ring oxygens. Both the electronic nature of the dienophile and the neighbouring group non-bonded interactions contribute to the success of these cycloadditions.Key words: magnesium chelate, Lewis acid, intramolecular Diels–Alder, cycloaddition.

Part 2: Efficient strategies for the construction of variably substituted bicyclo[5.3.1]undecenones (AB-taxane ring systems) and their conversion to tricyclo[9.3.1.03,8]pentadecenones (ABC taxane ring systems) and bicyclo[2.2.2]octanones

2004 ◽  
Vol 82 (2) ◽  
pp. 227-239 ◽  
Author(s):  
Nidia P Villalva-Servín ◽  
Alain Laurent ◽  
Alex G Fallis
Keyword(s):  
Lewis Acid ◽  
Sigmatropic Rearrangement ◽  
Diels Alder ◽  
Direct Access ◽  
Cope Rearrangement ◽  
Ring Closing Metathesis ◽  
Ring Systems ◽  
Sigmatropic Rearrangements ◽  
Key Words Magnesium ◽  
Cope Rearrangements

The extension of our strategies for the construction of cyclic molecules containing variably substituted bicyclo[5.3.1]undecenones (AB taxane ring systems) for the synthesis of the tricyclo[9.3.1.03,8]pentadecenone (ABC taxane ring system) and bicyclo[2.2.2]octanones are described. These routes employ a multi-component coupling protocol that employs sequential magnesium-mediated carbometallation of allyl-substituted propargyl alcohols followed by diastereoselective Lewis acid catalyzed intramolecular Diels–Alder reactions (IMDA). Subsequent ring-closing metathesis (RCM) afforded the ABC taxane core structure. Enone accelerated [3,3] sigmatropic rearrangements (Cope rearrangements) generated the bicyclo[2.2.2]octanone nucleus. In the presence of a Lewis acid, the dienophile precursor underwent a tandem reaction via the adduct directly to the bicyclo[2.2.2]octanones. This is the first example of a novel enone accelerated carbocycle Cope rearrangement and provides direct access to bicyclo[2.2.2]octanones by a new route that compliments the traditional cyclohexadiene cycloaddition approach. Key words: magnesium chelate, Lewis acid, taxanes, Diels–Alder, sigmatropic rearrangement, oxy-Cope, ring-closing metathesis, bicyclo[2.2.2]octanone.

Stereochemical Aspects of Aldehyde Additions to Cyclohex-2-Enylstannanes

1985 ◽  
Vol 38 (12) ◽  
pp. 1767 ◽  
Author(s):  
D Young ◽  
W Kitching
Keyword(s):  
Lewis Acid ◽  
Boron Trifluoride ◽  
Boron Trifluoride Etherate ◽  
Alcohol Formation ◽  
Acid Adduct

Cyclohex-2-enylation of aldehydes, mediated with boron trifluoride etherate, involves γ-equatorial approach of the presumed aldehyde-Lewis acid adduct (RCHO-BF3), irrespective of starting stannane stereochemistry. Marginal threo selectivity characterizes homoallyl alcohol formation from benzaldehyde, whereas alkanals react with high erythro selectivity, so that 1-(1′-hydroxyalkyl)cyclohex-2-enes in this diastereomeric form are available based on allyltin chemistry.

Face-selective Diels–Alder reactions of (1R,5R)-3-formyl-6,6-dimethylbicyclo[3.1.1]hept-3-en-2-one

1994 ◽  
Vol 72 (9) ◽  
pp. 1883-1893 ◽  
Author(s):  
Hsing-Jang Liu ◽  
Yanhong Li ◽  
Eric N.C. Browne
Keyword(s):  
Low Temperatures ◽  
Boron Trifluoride ◽  
General Type ◽  
Acid Catalysis ◽  
High Selectivity ◽  
Boron Trifluoride Etherate ◽  
Alder Reaction ◽  
Diels Alder ◽  
Diels Alder Reaction ◽  
Very High

The stereofacially differentiated enone aldehyde 11 was chosen to study the effects of steric and electronic influence on the Diels–Alder reaction. Under Lewis acid catalysis, 11 adds to dienes at low temperatures at a reasonable rate. Yields of desired chiral adducts are good to high with zinc chloride and boron trifluoride etherate catalysis. In all cases only products of addition to the Re face of general type 27 were observed. The regiochemistry of the adducts is exclusively that predicted by the ortho and para rules. The stereochemistry shows a very high selectivity in favour of aldehyde-endo transition state products. Unusual byproducts were also obtained in some examples and mechanisms of these unexpected reactions are discussed.

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