Enantioselective ring opening of tropinone. A new entry into tropane alkaloids

1997 ◽  
Vol 75 (6) ◽  
pp. 754-761 ◽  
Author(s):  
Marek Majewski ◽  
Ryszard Lazny ◽  
Agnieszka Ulaczyk
Keyword(s):  
Ring Opening ◽  
Stereoselective Synthesis ◽  
Tropane Alkaloids ◽  
Amine Hydrochloride ◽  
Lithium Amides ◽  
Ring Opening Reaction ◽  
Alkyl Chloroformates ◽  
Optically Pure ◽  
Enantioselective Deprotonation

The lithium enolate of tropinone reacts with alkyl chloroformates to give 6-N-carboalkoxy-N-methyl-2-cycloheptenones (4). These compounds can be produced enantioselectively, in up to 95% ee, if chiral lithium amides (derived from optically pure amines 5–7) are used for deprotonation of tropinone in the presence of additives. The effect of additives such as LiCl, LiBr, LiF, LiClO4, CeCl3, ZnCl2, LiOH, TMEDA, HMPA, and DMPU on enantioselectivity of this deprotonation–ring opening sequence varies from slight to very large depending on the chiral amide – additive combination. Especially large increases in enantioselectivity are observed when the chiral, C2 symmetrical, lithium bis-α,α′-methylbenzylamide (Li-5a) is used with one equivalent of LiCl. This reagent is best generated in situ from the corresponding amine hydrochloride and n-BuLi (2 equiv.). The ring-opening reaction combined with transposition of the carbonyl group (via Wharton reaction or allylic oxidation) provides a new method of stereoselective synthesis of tropane alkaloids having a protected hydroxyl at C-6 or C-7 (6β- and 7β-acetoxytropanes 14a, b) and physoperuvine (19). Keywords: enantioselective deprotonation, tropane alkaloids.

Torque control by metal-orbital interactions

2006 ◽  
Vol 78 (2) ◽  
pp. 415-423 ◽  
Author(s):  
Masahiro Murakami ◽  
Yasufumi Miyamoto ◽  
Munehiro Hasegawa ◽  
Ippei Usui ◽  
Takanori Matsuda
Keyword(s):  
Transition State ◽  
Ring Opening ◽  
Stereoselective Synthesis ◽  
Torque Control ◽  
Orbital Interactions ◽  
Silicon Carbon ◽  
Highest Occupied Molecular Orbital ◽  
Ring Opening Reaction ◽  
Novel Method ◽  
Metal Orbital

The silyl substituent of 3-silylcyclobutene prefers inward rotation rather than outward rotation during a thermal ring-opening reaction, giving the Z-isomer predominantly. This intriguing behavior was explained by assuming electron-accepting interactions between the low-lying σ*-orbital of the silicon-carbon linkage and the highest occupied molecular orbital (HOMO) of the opening cyclobutene system, which are possible only in the inward transition state. On the basis of this finding, a novel method for the stereoselective synthesis of functionalized 1,3-butadiene derivatives from cyclobutenones was developed. Boryl substituents exhibit even stronger preference for inward rotation than silyl substituents as a result of electron delocalization from the cyclobutene HOMO into the vacant p-orbital of boron at the inward transition state.

Regio- and Stereoselective Synthesis of a Novel Family of Unsaturated Compounds with the S–Se Bond and Their Cyclization to 2,3-Dihydro-1,4-thiaselenines

Synthesis ◽  
2019 ◽  
Vol 51 (08) ◽  
pp. 1832-1840 ◽  
Author(s):  
Svetlana Amosova ◽  
Andrey Filippov ◽  
Vladimir Potapov ◽  
Maxim Penzik ◽  
Nataliya Makhaeva ◽  
...  
Keyword(s):  
Ring Opening ◽  
Room Temperature ◽  
Stereoselective Synthesis ◽  
Reaction Times ◽  
Nucleophilic Attack ◽  
Selenium Atom ◽  
Efficient Synthesis ◽  
Reaction Conditions ◽  
Ring Opening Reaction ◽  
Acid Catalyzed

Regio- and stereoselective ring-opening reaction of 2-bromomethyl-1,3-thiaselenole with thiols proceeded as nucleophilic attack at the selenium atom of seleniranium intermediate affording unsaturated selanyl sulfides, (Z)-CH2=CHSCH=CHSeSR, in up to 93% yield. Dithiols were involved in this reaction giving symmetrical polyunsaturated compounds with two S–Se bonds in 70–75% yields. Efficient synthesis of 2-(organylsulfanyl)-2,3-dihydro-1,4-thiaselenines in 69–96% yields was developed by the acid-catalyzed cyclization of the unsaturated selanyl sulfides. Mild reaction conditions (room temperature) and short reaction times are important features of this methodology.

scholarly journals PhSeZnCl in the Synthesis of Steroidal β-Hydroxy-Phenylselenides Having Antibacterial Activity

2019 ◽  
Vol 20 (9) ◽  
pp. 2121 ◽  
Author(s):  
Jastrzebska ◽  
Mellea ◽  
Salerno ◽  
Grzes ◽  
Siergiejczyk ◽  
...  
Keyword(s):  
Antibacterial Activity ◽  
Biofilm Formation ◽  
Ring Opening ◽  
Antibacterial Properties ◽  
Multidrug Resistant ◽  
Bacterial Biofilm ◽  
Resistant Bacteria ◽  
Multidrug Resistant Bacteria ◽  
Ring Opening Reaction

We report here the reaction of in situ prepared PhSeZnCl with steroid derivatives having an epoxide as an electrophilic functionalization. The corresponding ring-opening reaction resulted to be regio- and stereoselective affording to novel phenylselenium-substituted steroids. Assessment of their antibacterial properties against multidrug-resistant bacteria, such as Pseudomonas aeruginosa Xen 5 strain, indicates an interesting bactericidal activity and their ability to prevent bacterial biofilm formation.

Morphologies and Mechanical Properties of Epoxy Resin/Polymethyl Methacrylate Interpenetrating Network Modified with Kaolin

2011 ◽  
Vol 337 ◽  
pp. 184-187
Author(s):  
Gui Xiang Hou ◽  
Xiao Ai Chen ◽  
Xiao Ming Sang
Keyword(s):  
Epoxy Resin ◽  
Polymethyl Methacrylate ◽  
Ring Opening ◽  
Interpenetrating Network ◽  
Scanning Electronic Microscopy ◽  
Epoxy Ring ◽  
Ring Opening Reaction ◽  
Epoxy Ring Opening ◽  
Lower Tensile Strength

Epoxy resin/polymethyl methacrylate(EP/PMMA,70/30) interpenetrating network composites containing various contents of dimethyl sulfoxide modified kaoline (EP/PMMA /K-DMSO) composites were prepared by a sequential polymeric technique and an in situ intercalation method. FTIR results showed that the epoxy ring opening reaction occurs, the formation of IPN structure of PMMA and EP has been created. The structure of composite material was characterized by scanning electronic microscopy (SEM). The result indicated that higher impact strength and lower tensile strength with increasing concentration of K-DMSO.

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