- Enantioselective halogenative semi-pinacol rearrangement: Extension of substrate scope and mechanistic investigations
-
The present Full Paper article discloses a survey of our recent results obtained in the context of the enantioselective halogenation-initiated semi-pinacol rearrangement. Commencing with the fluorination/semi-pinacol reaction first and moving to the heavier halogens (bromine and iodine) second, the scope and limitations of the halogenative phase-transfer methodology will be discussed and compared. An extension of the fluorination/semi-pinacol reaction to the ring-expansion of five-membered allylic cyclopentanols will be also described, as well as some preliminary results on substrates prone to desymmetrization will be given. Finally, the present manuscript will culminate with a detailed mechanistic investigation of the canonical fluorination/semi-pinacol reaction. Our mechanistic discussion will be based on in situ reaction progress monitoring, complemented with substituent effect, kinetic isotopic effect and non-linear behaviour studies.
- Romanov-Michailidis, Fedor,Romanova-Michaelides, Maria,Pupier, Marion,Alexakis, Alexandre
-
supporting information
p. 5561 - 5583
(2015/03/30)
-
- Enantioselective organocatalytic fluorination-induced Wagner-Meerwein rearrangement
-
Cracked under strain: Strained allylic cyclobutanols and cyclopropanols readily undergo a ring expansion described by the title rearrangement. This reaction is promoted by catalytic amounts of 1 and displays high tolerance with respect to the substrate scope. The corresponding β-fluoro spiroketone products are isolated in high yields and with excellent stereoselectivities. EDG=electron-donating group, EWG=electron-withdrawing group. Copyright
- Romanov-Michailidis, Fedor,Guénée, Laure,Alexakis, Alexandre
-
supporting information
p. 9266 - 9270
(2013/09/12)
-
- Enantioselective organocatalytic iodination-initiated Wagner-Meerwein rearrangement
-
The present manuscript describes a high-yielding enantioselective semipinacol transposition, initiated by an electrophilic iodination event. The title transformation makes use of the anionic phase-transfer catalysis (PTC) paradigm for chirality induction. Thus, when combined appropriately, the insoluble cationic iodinating reagent S9 and the lipophilic phosphoric acid L9 act as an efficient source of chiral iodine that performs the semipinacol transposition of strained allylic alcohols A x to β-iodo spiroketones Bx in good yields and with high levels of diastereo- and enantio-induction. The product β-iodo spiroketones could be derivatized stereospecifically and without stereoerosion, giving rise to products inaccessible directly from a semipinacol rearrangement.
- Romanov-Michailidis, Fedor,Guenee, Laure,Alexakis, Alexandre
-
supporting information
p. 5890 - 5893
(2013/12/04)
-
- A New and Practical Five-Carbon Component for Metal-Catalyzed [5 + 2] Cycloadditions: Preparative Scale Syntheses of Substituted Cycloheptenones
-
(Matrix Presented) Described herein is an efficient preparative scale synthesis of 1-(2-methyoxyethoxy)-1-vinylcyclopropane and the investigation of the utility of this reagent as a new five-carbon component in metal-catalyzed [5 + 2] cycloadditions. A new cycloaddition procedure is also described that proceeds up to 12-fold faster and with 10-fold less catalyst than previously described, providing cycloheptenones in many cases in minutes and in isolated yields of 75-97%. The procedure is readily conducted on a small or large scale (up to 100 mmol thus far).
- Wender, Paul A.,Dyckman, Alaric J.,Husfeld, Craig O.,Scanio, Marc J. C.
-
p. 1609 - 1611
(2007/10/03)
-
- Process for production of 1-alkoxy-1-trimethylsilyloxy cyclopropanes
-
The present invention provides a process for producing 1-alkoxy-1-trimethylsilyloxycyclopropane represented by the following general formula: STR1 by reacting microgranular metallic sodium dispersed in a hydrocarbon solvent, β-halogenocarboxylic acid ester represented by the following general formula: STR2 and chlorotrimethylsilane. According to the present invention, by using no ether compound solvent (the ether compound solvent has various problems in safety) and using microgranular metallic sodium dispersed in a hydrocarbon solvent, 1-alkoxy-1-trimethylsilyloxycyclopropane can be industrially produced simply (no special apparatus is required) at an advantageous cost at a yield at least equal to that obtained when an ether is used as solvent.
- -
-
-
- Kinetics of Cyclopropyl Radical Reactions. 3. Study of Some 1-Substituted Cyclopropyl Radicals by EPR Spectroscopy. The Inversion Barrier for 1-Methylcyclopropyl
-
The 1-methyl-, 1-ethoxy-, and 1-chlorocyclopropyl radicals have been observed by low-temperature EPR spectroscopy in "frozen" configurations in which the ring hydrogens that are syn and anti to the unpaired elecron's orbital have different hyperfine splittings.The aH(syn)/aH(anti) ratios are 1.5 (CH3), 1.8 (EtO), and 1.9 (Cl), all considerably lower than the ratio of ca. 3.3 found by Kawamura et al. for methyl-substituted 1-fluorocyclopropyl radicals.The out-of-plane angles of the 1-substituent have been calculated from measured a13Cα values to be 22.5 deg (cyclopropyl), 22.9 deg (CH3), 29.1 deg (EtO), and 5.8 deg (MeSi).These angles are considerably smaller than those that have been calculated for some of these radicals by ab initio and other methods.Variable-temperature EPR spectroscopy on 1-methylcyclopropyl yields the following Arrhenius equation for its inversion: log (kinv/s-1) = (13.1 +/- 0.3) - (3.1 +/- 0.2)/2.3RT kcal/mol.For 1-ethoxycyclopropyl the rate constant for rotation about the .C-OEt bond can be represented by log (krot/s-1) = (12.5 +/- 0.2) - (5.8 +/- 0.2)/2.3RT.The barrier to inversion of this radical is >/= 9 kcal/mol.The 1-chlorocyclopropyl radical could only be observed at very low temperatures.
- Deycard, S.,Hughes, L.,Lusztyk, J.,Ingold, K. U.
-
p. 4954 - 4960
(2007/10/02)
-
- Reactions of the Cyclopropanone Hemiketal Magnesium Salt with Some Nucleophilic Reagents
-
Cyclopropanol (5), 1-(arylethynyl)cyclopropanol (7), 1-(3-hydroxypropyl)cyclopropanol derivative 10, 1-(2-propynyl)cyclopropanol (14), cyclopropanone cyanohydrin (19), 1-(aminomethyl)cyclopropanol (21) derivatives, benzylidenecyclopropanes 32, and ethyl cyclopropylideneacetate (38) have been prepared from the magnesium salt of cyclopropanone hemiketal 3. 3-Cyclopropylidene-1-propanol (12) and 3-cyclopropylidene-1-propyne (16) have been obtained from the cyclopropanols 10 and 14, respectively. Some reactions of this new synthon were specific. On the other hand, 3 did not undergo the nucleophilic addition of sulfur and nitrogen ylides; it underwent oxidizing ring opening with BrZnCH2COOEt and induced the decomposition of diazomethane.
- Salauen, Jacques,Bennani, Fatima,Compain, Jean-Claude,Fadel, Antoine,Ollivier, Jean
-
p. 4129 - 4135
(2007/10/02)
-
