Enamines: recent advances in synthetic, spectroscopic, mechanistic, and stereochemical aspects—I

Oxidative cleavage of silicon-carbon bonds in organosilicon fluorides to alcohols

This work reports ESR studies that identify the favored site of deprotonation of the guanine cation radical (G•+) in an aqueous medium at 77 K. Using ESR and UV−visible spectroscopy, one-electron oxidized guanine is investigated in frozen aqueous D2O solutions of 2‘-deoxyguanosine (dGuo) at low temperatures at various pHs at which the guanine cation radical, G•+ (pH 3−5), singly deprotonated species, G(−H)• (pH 7−9), and doubly deprotonated species, G(−2H)•- (pH > 11), are found. C-8-deuteration of dGuo to give 8-D-dGuo removes the major proton hyperfine coupling at C-8. This isolates the anisotropic nitrogen couplings for each of the three species and aids our analyses. These anisotropic nitrogen couplings were assigned to specific nitrogen sites by use of 15N-substituted derivatives at N1, N2, and N3 atoms in dGuo. Both ESR and UV−visible spectra are reported for each of the species:  G•+, G(−H)•, and G(−2H)•-. The experimental anisotropic ESR hyperfine couplings are compared to those obtained from DFT ...

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The Guanine Cation Radical: Investigation of Deprotonation States by ESR and DFT

The addition of aldehydes and ketones to alkenes in the presence of Bronsted acids is usually called the Prins reaction.1,2 Addition of the protonated carbonyl compound to the alkene gives a β-hydroxy carbocation which reacts with a nucleophile such as chloride, water or acetate to give (1), adds to a second molecule of aldehyde to give (2) or loses a proton to give homoallylic alcohol (3; Scheme 1). Formaldehyde and electron-deficient carbonyl compounds undergo concerted thermal ene reactions with alkenes at temperatures ranging from 100 to 200 °C to give homoallylic alcohols (equation 1; R1 = H, CCl3, or CO2R).3–7 A wide variety of carbonyl compounds undergo Lewis acid catalyzed reactions with alkenes to give homoallylic alcohol ene adducts in excellent yield with high selectivity, although in some cases γ-chloro alcohols are formed as by-products.8,9 Recent investigations suggest that at least some of these Lewis acid catalyzed ene reactions are stepwise, rather than concerted, but that the intermediate bears more resemblance to a π-complex than to the open carbocation intermediate in the Prins reaction.

The Prins and Carbonyl Ene Reactions

David S. Weinberg

Papers

Mass Spectrometry in Structural and Stereochemical Problems. LXXXVIII.1 Rearrangements of Simple Terpenes on Electron Impact2

Bimolecular Displacement Reactions. I. Reaction of endo-Norbornanol and 7-Norbornanol with Triphenylphosphine and Bromine

Secondary isotope effects in the solvolysis of norbornyl bromides

Mass Spectrometry in Structural and Stereochemical Problems. CXII.1 Fragmentation of Two Bicyclic Amines on Electron Impact2a

Condensation of internal olefins with paraformaldehyde and hydrogen chloride [yielding tetrahydropyrans]