Mechanism of Acetal Cleavage with Methylmagnesium Iodide

1985 ◽  
Vol 38 (7) ◽  
pp. 1031
Author(s):  
AD Abell ◽  
RA Massy-Westropp
Keyword(s):  
Grignard Reagent ◽  
Tertiary Alcohol ◽  
Methyl Group ◽  
Methylmagnesium Iodide ◽  
Oxygen Bond

The reaction of methylmagnesium iodide with methyl (1R,3S,5R)-1-(furan- 3′-yl)-5-methyl-2,8-dioxabicyclo[3.2.1]octane-3-carboxylate (2) gives products arising from regioselective carbon-oxygen bond fission and intermolecular transfer of the methyl group of the Grignard reagent to the intermediate oxocarbonium ion, in addition to the usual tertiary alcohol.

The Baran Synthesis of Vinigrol

2013 ◽  
Author(s):  
Douglass F. Taber
Keyword(s):  
Free Radical ◽  
Diels Alder ◽  
Tertiary Alcohol ◽  
Hydroxy Ketone ◽  
Oxide Reduction ◽  
Relative Configuration ◽  
Methyl Group ◽  
Radical Reduction ◽  
Grob Fragmentation ◽  
La Jolla

The diterpene vinigrol 3, isolated from Virgaria nigra F-5408, has eluded total synthesis for more than 20 years. Attempts to construct the four-carbon bridge on a preformed cis-decalin have been unavailing. Phil S. Baran of Scripps/La Jolla solved (Angewandte Chem. Int. Ed. 2008, 47, 3054; J. Am. Chem. Soc. 2009, 131, 17066) this problem by adding the extra C-C bond of 1, which could then be cleaved in course of a Grob fragmentation, leading to 2. The preparation of 1 started with the dihydroresorcinol derivative 4. Diels-Alder addition of the ester 5 gave 6, with a modest 2:1 dr. Addition of allyl MgCl to the derived aldehyde 7 proceeded with 6:1 dr. The resulting triene was conformationally sufficiently constrained that cyclization to 8 proceeded at room temperature over 2 weeks, or more conveniently at 105°C for 90 minutes. With 8 in hand, oxidation to the ketone allowed installation of the additional methyl group of 9. Desilylation followed by OH-directed reduction set the relative configuration of 1 correctly for the Grob fragmentation to the Z -alkene 2. There were two remaining problems in the synthesis. The alkene of 2 had to be converted to the methylated tertiary alcohol, and the ketone had to be elaborated to the ene diol. Though seemingly straightforward, the congested tricyclic skeleton of 2 made many common transformations difficult. The solution to the first problem was found in the selective dipolar addition of bromonitrile oxide. Reduction of the ketone then enabled HO-directed hydrogenation of the alkene, which otherwise was resistant. Dehydration followed by reduction with LiAlH4 gave the desired methyl group bearing a primary amine, which was removed by free radical reduction of the corresponding isonitrile, to give 12. With 12 in hand, the end of the synthesis appeared to be in sight. In fact, the reduction of a variety of oxidized intermediates proved difficult. In the end, a sequence that did not require reduction proved effective. Dihydroxylation of 12 gave a diol, selective oxidation of which delivered the α-hydroxy ketone 13. Formation of the trisylhydrazone followed by Shapiro reaction gave the intermediate alkenyl anion, which was trapped with formaldehyde to give the long-sought vinigrol 3.

Behaviour of 2′-O-p-toluenesulfonyl uridine towards excess of a Grignard reagent

1989 ◽  
Vol 67 (4) ◽  
pp. 708-709 ◽  
Author(s):  
Annie Grouiller ◽  
Hassan Essadiq
Keyword(s):  
Grignard Reagent ◽  
Grignard Reaction ◽  
Methylmagnesium Iodide

Two C-methylated base nucleosides were obtained when 2′-O-tosyl-5′-O-trityluridine was reacted with 30 equivalents of methylmagnesium iodide. Keywords: nucleoside, Grignard reaction, C-methyl pyrimidinone, anhydro derivative, arabinofuranosyl.

Alkyl-oxygen bond cleavage in trityl acetate-O18 during reaction with phenyl Grignard reagent

1969 ◽  
Vol 34 (9) ◽  
pp. 2500-2503 ◽  
Author(s):  
K. Darrell Berlin ◽  
Russell D. Shupe ◽  
Ronald D. Grigsby
Keyword(s):  
Grignard Reagent ◽  
Bond Cleavage ◽  
Oxygen Bond

Use of [13C-methyl]Tropinone to follow the fate of the methyl group during calystegine formation in root cultures of Solanum dulcamara (Solanaceae)

Planta Medica ◽  
2008 ◽  
Vol 74 (09) ◽  
Author(s):  
TA Bartholomeusz ◽  
R Molinié ◽  
A Roscher ◽  
AC Freydank ◽  
B Dräger ◽  
...  
Keyword(s):  
Root Cultures ◽  
Solanum Dulcamara ◽  
Methyl Group

STEROIDSTRUKTUR UND LEBERTOXIZITÄT

1967 ◽  
Vol 54 (1) ◽  
pp. 73-84 ◽  
Author(s):  
H. L. Krüskemper ◽  
G. Noell
Keyword(s):  
Alkaline Phosphatase ◽  
Liver Function ◽  
Blood Coagulation ◽  
Electrophoretic Pattern ◽  
Coagulation Factors ◽  
Blood Coagulation Factors ◽  
Methyl Group ◽  
Liver Functions ◽  
Male Subjects ◽  
Androstane Derivatives

ABSTRACT In male subjects investigations have been carried out regarding the effect of C1- and C17-methylated androstane derivatives (20 mg per day, orally, two weeks) on liver functions (parameters: activities of GPT, GOT, alkaline phosphatase and cholinesterase in serum; electrophoretic pattern; blood coagulation factors V, VII, X and prothrombin; BSP-retention). In addition to the well known hepatotropic action of 17α-alkylated C-19-steroids a quasi-axial 1α-methyl configuration (in 1α-methylandrost-2-en-17β-ol) definitely increased BSP-retention and several coagulation factors. These steroid effects decreased gradually when a methyl group was introduced in C1 equatorially (1-methylandrost-1-en-17β-ol-3-one) or quasi-equatorially (1β-methylandrost-2-en-17β-ol), the latter compound completely lacking from any influence on parameters of liver function under investigation.

Oxygen-Oxygen Bond Cleavage and Formation in Co(II) Mediated Stoichiometric O2 Reduction via the Potential Intermediacy of a Co(IV) Oxyl Radical

2018 ◽  
Author(s):  
Lucie Nurdin ◽  
Denis M. Spasyuk ◽  
Laura Fairburn ◽  
Warren Piers ◽  
Laurent Maron
Keyword(s):  
Bond Cleavage ◽  
Peroxo Complex ◽  
Oxygen Oxygen ◽  
O2 Reduction ◽  
Oxygen Bond ◽  
Pentadentate Ligand

Diprotonation of a remarkably stable, toluene soluble cobalt peroxo complex supported by a neutral, dianionic pentadentate ligand leads to facile O-O bond cleavage and production of a highly reactive Co(IV) oxyl cation intermediate that dimerizes and releases O<sub>2</sub>. These processes are relevant to both O<sub>2</sub> reduction and O<sub>2</sub> evolution and the mechanism was probed in detail both experimentally and computationally.

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