Six groups of ω-ethyl-, ω-ethenyl- and ω-ethynyl-α-alkylidene-γ-lactones

Total Syntheses of 3-epi-Litsenolide D2 and Lincomolide A

“…This investigation revealed several reports on α,β′-conjugated γ-lactone derivatives bearing 3-hydroxy and 4-methyl groups, a small fraction of which has been depicted in Figure . ,− Given the relationship between the structure and the physical property, two notable features can be observed that are as follows: (1) the chemical shifts of the vinyl protons at the C6 position clearly revealed that the exo -alkene moiety of the γ-lactone derivatives can exhibit either the Z - or E -form. Namely, the protons in the Z -form geometry ranged from 6.54 to 6.56 ppm (see litsenolides C 1 and D 1 , 4- epi -litsenolide C 1 , and licunolide A), whereas the protons in E -form geometry ranged from 6.93 to 7.01 ppm (Figures and ); (2) only the structures bearing a hydroxy group with R -configuration at the C3 position exhibited dextrorotatory specific rotation ([α] 24 D +77.1, see ent -isodihydromahubenolide B vs. all the others with S -configuration of levorotatory in Figure and those in previous reports). Therefore, it seems reasonable to conclude that we accomplished the total synthesis of 3- epi -litsenolide D 2 ( 1 ) and that the reported specific rotation of 1 was inaccurate.…”

Asymmetric Synthesis of α-Alkylidene-β-hydroxy-γ-butyrolactones via Enantioselective Tandem Michael–Aldol Reaction

“…HRMS (EI): m / z calcd for C 17 H 28 O 3 280.2038, found 280.2038. [α] 20 D = −15.79 ( c 0.7, dioxane; lit 7. [α] 24 D = −2.4, dioxane).…”

“…The spectroscopic data and specific rotation of the synthetic samples of 1 and 9 ( 1 H, 13 C NMR) were in full agreement with those reported in the literature. In the same manner, the cross-coupling of ent - 8a from ( S )-β-iodo MBH ester with suitable Grignard reagent produced ( Z )-α-alkylidene butyrolactones 10 , 11 , and (+)-dihydromahubenolide ( 2 ) in excellent yields of 97%, 85%, and 83%, respectively (Scheme ).…”

“…The cross-coupling of 8a with undec-10-enylmagnesium bromide in the catalytic presence of LiCuBr 2 produced (−)-litsenolide A 1 ( 1 ) ,, in 56% yield while coupling with n -tridecanylmagnesium bromide afforded (−)-litsenolide C 1 ( 9 ) ,− in 78% yield without changing olefinic geometry (Scheme ). The spectroscopic data and specific rotation of the synthetic samples of 1 and 9 ( 1 H, 13 C NMR) were in full agreement with those reported in the literature.…”