Synthesis of Enantiomerically Puretrans-1,2-Disubstituted Cyclopentanes and Cyclohexanes by Intramolecular Allylsilane Addition to Chiral Alkylidene-1,3-dicarbonyl Compounds

Total Synthesis of (−)-Nakadomarin A

“…This thermodynamic control has been previously observed in related systems 14 and can be rationalized by better overlap of the ester and adjacent double bond in E -amide 7 , in contrast to the carbonyls of the corresponding Z-amide, both of which would be twisted out of conjugation. Much to our delight, heating amide 9 and furaldehyde 8 in benzene in the presence of benzoic acid and piperidine delivered the E -configurational isomer 7 as the sole product in 87% yield (Scheme 6).…”

“…On the basis of observations made during our model system study, we anticipated that Knoevenagel condensation between amide 9 and furaldehyde 8 would provide unsaturated amide 7 , possessing the requisite E -geometry for the cyclization to tetracycle 5 . This thermodynamic control has been previously observed in related systems and can be rationalized by better overlap of the ester and adjacent double bond in E -amide 7 , in contrast to the carbonyls of the corresponding Z-amide, both of which would be twisted out of conjugation. Much to our delight, heating amide 9 and furaldehyde 8 in benzene in the presence of benzoic acid and piperidine delivered the E -configurational isomer 7 as the sole product in 87% yield (Scheme ).…”

Lewis Acid-Promoted Cyclization Reactions of Alkenyl Ethenetricarboxylates: Stereoselective Synthesis of 2-Oxotetrahydrofurans and 2-Oxopyrrolidines

“…We have developed Lewis acid-promoted stereoselective cyclization of alkynyl ethenetricarboxylates with high generality (eq 2) . Lewis acid-promoted intramolecular ene reaction and related cyclization of silicon-substituted allylic alkylidene 1,3-dioxo compounds to give carbocycles have also been reported. Furthermore, Lewis acid-promoted addition of simple alkenes to aldehydes proceeding to form C–C bonds (Prins reaction) is well-known .…”

Lewis Acid Promoted Cyclization of Enyne Triesters and Diesters

“…Lewis acid promoted reactions have been extensively utilized for ring-forming reactions such as Diels−Alder reactions, [2 + 2] cycloadditions, ene reactions, and alkene−alkene cyclizations . Lewis acids play a major role in carbon−carbon bond-forming processes by coordinating to carbonyl compounds .…”

“…On the other hand, only a few examples of Lewis acid promoted cyclizations of enynes have been reported so far. Snider and Roush reported an example of cyclization of propargylic esters of ethenetricarboxylic acid 1 in the presence of FeCl 3 as an extension of ene−ene cyclization to give chlorinated γ-lactones (eq 1) 4a. Recently, we have reported ZnBr 2 (THF)-promoted cycloisomerizations of enynes 1 to give exocyclic conjugated dienes 12 (eq 2) …”