Neighboring Hydroxyl Group-Assisted Allylboration and Lewis Acid-Mediated Carbonyl-Ene Reaction for Access to a Hapalindole Cyclohexane Core with Multiple Contiguous Stereogenic Centers

2019 ◽  
Vol 84 (3) ◽  
pp. 1605-1613 ◽  
Author(s):  
Lu Li ◽  
Zhao Yang ◽  
Jiao Yang ◽  
Quanzheng Zhang ◽  
Qiuyuan Tan ◽  
...  
Keyword(s):  
Lewis Acid ◽  
Hydroxyl Group ◽  
Ene Reaction ◽  
Stereogenic Centers

ChemInform Abstract: Lewis Acid Catalyzed Intramolecular Direct Ene Reaction of Indoles.

ChemInform ◽  
2011 ◽  
Vol 42 (18) ◽  
pp. no-no
Author(s):  
Bo Han ◽  
You-Cai Xiao ◽  
Yuan Yao ◽  
Ying-Chun Chen
Keyword(s):  
Lewis Acid ◽  
Ene Reaction ◽  
Acid Catalyzed

Lewis Acid Catalyzed Intramolecular Direct Ene Reaction of Indoles

2010 ◽  
Vol 122 (52) ◽  
pp. 10387-10389 ◽  
Author(s):  
Bo Han ◽  
You-Cai Xiao ◽  
Yuan Yao ◽  
Ying-Chun Chen
Keyword(s):  
Lewis Acid ◽  
Ene Reaction ◽  
Acid Catalyzed

Lewis Acid-Promoted Intermolecular Carbonyl-ene Reaction of Enantiopure 4-Oxoazetidine-2-carbaldehydes. Rapid Entry to Novel Fused Polycyclic β-Lactams

2003 ◽  
Vol 68 (8) ◽  
pp. 3106-3111 ◽  
Author(s):  
Benito Alcaide ◽  
Pedro Almendros ◽  
Carmen Pardo ◽  
Carolina Rodríguez-Ranera ◽  
Alberto Rodríguez-Vicente
Keyword(s):  
Lewis Acid ◽  
Ene Reaction

scholarly journals Stereoselective Synthesis of Highly-Congested Tetralin-Fused Spirooxindoles with Hydroxyl Group: Net Oxygen Atom Induced Hydride Shift/cyclization Process.

2021 ◽  
Author(s):  
Dan Sakai ◽  
mizuki machida ◽  
Keiji Mori
Keyword(s):  
Reaction Mechanism ◽  
Nitrogen Atom ◽  
Oxygen Atom ◽  
Stereoselective Synthesis ◽  
Hydroxyl Group ◽  
Target Structure ◽  
Hydride Shift ◽  
Cyclization Process ◽  
Stereogenic Centers

Highly stereoselective synthesis of tetralin-fused spirooxindoles with two contiguous stereogenic centers. In the present reaction, not only [1,5]-hydride shift/cyclization process, but also replacemnt of nitrogen atom to oxygen atom ocurred smoothly to give target structure with hydroxy grop in good chemical yields with good to excellent diastereoselectivities (up to d.r. = >20:1). Investigation of the reaction mechanism suggested that this “atom-replacement” event ocurred via the iminium cation intermediates.

Microwave-assisted Claisen Rearrangement of 1-Allyloxy-4-hydroxybenzene in the Presence of Metal Salt

2021 ◽  
Vol 07 ◽  
Author(s):  
Fumiyoshi Ozaki ◽  
Yutaka Okada
Keyword(s):  
Alkali Metal ◽  
Lewis Acid ◽  
Claisen Rearrangement ◽  
Metal Salt ◽  
Alkali Metal Salt ◽  
Metal Salts ◽  
Hydroxyl Group ◽  
Microwave Assisted ◽  
Ethereal Oxygen

: Microwave-assisted Claisen rearrangement of allyloxybenzene with a hydroxyl group was conducted in the presence of metal salts. The rearrangement was promoted in the presence of an alkali metal salt, because the reaction substrate was converted to a phenoxide-type ion, which can efficiently absorb microwaves. In contrast, a Lewis acid was strongly coordinated to the ethereal oxygen, and this structure could also absorb microwaves efficiently.

The Corey Synthesis of (+)-Lupeol

2013 ◽  
Author(s):  
Douglass F. Taber
Keyword(s):  
Lewis Acid ◽  
Ring Closure ◽  
Aryl Ether ◽  
Asymmetric Dihydroxylation ◽  
Effi Ciency ◽  
Stereogenic Centers ◽  
Enantioselective Epoxidation ◽  
Subsequent Cyclization ◽  
Acidic Conditions ◽  
Robinson Annulation

The total synthesis of lupeol was one of the crowning achievements of the Robinson annulation/ reductive alkylation approach to stereocontrolled polycarbocyclic construction developed by Gilbert Stork (J. Am. Chem. Soc. 1971, 93, 4945). It is a measure of the progress of organic synthesis since that time that E. J. Corey of Harvard University could devise (J. Am. Chem. Soc. 2009, 131, 13928) an enantioselective synthesis of (+)-lupeol 3 that could be carried out by a single colleague. The key step in the synthesis was the Lewis acid–mediated cyclization of 1 to 2. The preparation of 1 began with the enantioselective epoxidation of farnesol acetate 4. To this end, asymmetric dihydroxylation delivered the diol 5. Selective mesylation followed by exposure to dilute methoxide effected ring closure to the epoxide, but also removed the acetate, so this had to be reapplied. The synthesis of the aromatic portion of 1 started with the phenol 7. Protection as the very bulky triisopropylsilyl ether was important for the success of the subsequent cyclization, perhaps because it discouraged complexation of the Lewis acid with the aryl ether. Metalation followed by formylation delivered the aldehyde 8, which was reduced and carried on to the bromide 9. The derived Grignard reagent coupled smoothly with 6 under Li2CuCl4 catalysis. The cyclization of 1 to 2 proceeded with remarkable efficiency (43%!), for a reaction in which three new C-C bonds, four rings, and five new stereogenic centers were established. It is particularly noteworthy that the cyclization cleanly set the trans, anti, trans, anti tetra-cyclic backbone of (+)-lupeol 3. To complete the synthesis of 3, the less substituted alkene of 2 was selectively hydrogenated, then CH3 Li was added to give 10. Hydrolysis and dehydration yielded 11, which was reduced and equilibrated to 12. On brief exposure to MsCl/Et3 N, 13 cyclized to (+)-lupeol 3. It is a measure of the remarkable effi ciency of this synthesis of (+)-lupeol 3 that it provided suffi cient material to enable studies of the rearrangement of 3 under acidic conditions to other pentacyclic triterpenes, including, inter alia, germanicol, α -amyrin, δ -amyrin, and taraxasterol 14 .

Changes in ene reaction mechanisms with Lewis acid catalysis

1981 ◽  
Vol 46 (10) ◽  
pp. 2200-2201 ◽  
Author(s):  
L. M. Stephenson ◽  
Michael Orfanopoulos
Keyword(s):  
Lewis Acid ◽  
Reaction Mechanisms ◽  
Acid Catalysis ◽  
Lewis Acid Catalysis ◽  
Ene Reaction
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