Tandem Reduction-Aldol Reactions Induced by Stryker's Reagent

The incorporation of tandem reactions into a synthetic plan is an important strategy to achieve an efficient synthesis. Consecutive transformations of a substrate in a one-pot synthesis multiplies the complexity of the product while reducing the overall number of steps in the synthetic pathway.     

Time-resolved resonance Raman observation of the 2-fluorenylnitrenium ion reaction with guanosine to form a C8 intermediate

Time-resolved resonance Raman spectroscopy was used to directly observe the reaction of the 2-fluorenylnitrenium ion with guanosine to produce a C8 intermediate species. Comparison of the Raman spectra with results of density functional theory calculations indicates the C8 intermediate forms two C=N conjugated bonds in ring 1 of the guanosine moiety.     

Isoprene functionalisation : Chlorination of C10-isoprenoid sulfones with hexachloro-ethane

Lithiation of the sulfones 1–3 in THF at ?78° with lithium diisopropyl amide (LDA) is regioselective, since deuteration of the α-lithiosulfone 4 results in formation of the α-monodeuteriated sulfone 7. Higher temperature causes an intramolecular 1,4-addition of the lithiated sulfone 4 to the lithiated cyclic sulfone 19 and an intermolecular 1,4-addition of the lithiated sulfones 5 and 6. The cyclisation of Z-sulfone 1 has been used for the isolation of the isomeric E-sulfone 2 from mixtures of 1 and 2. The lithiated sulfones 4–6 are chlorinated with hexachloroethane (HCE). Due to acid/base reactions the α,α-dichlorinated cyclic sulfone 23 and α,α'-dichlorinated butadienyl sulfones 13–15 are formed in small amounts.     

Synthesis of homochiral 2‐C‐trifluoromethyl D‐and L‐ribose via trifluoromethylation of pentopyranosid‐2‐uloses

Efficient syntheses of 2‐C‐trifluoromethyl D‐ and L‐ribose and some O‐glycosides via trifluoromethylation of D‐ and L‐3,4‐O‐isopropylidene‐β‐erythro‐pentopyranosid‐2‐ulose with Ruppert's reagent are described.     

The Photoreversible Addition of Sulfur Dioxide to Benzobenzvalene: A new Approach to the Benzoprefulvene Biradical

Benzobenzvalene (naphthvalene; 1 ) is shown to add SO₂ to a lateral bicyclobutane bond with formation of a sulfone 2 and a ‘γ-sultine’ 3 . The structure of the latter is unambiguously established by X-ray diffraction. Both adducts extrude SO₂ upon direct photolysis at 254 nm and regenerate 1 accompanied by naphthalene in a 1:3 ratio. This result is interpreted in terms of a reversible homolytic cleavage leading, for both, 2 and 3 , to the same sulfinyloxy biradical 5 , which by loss of SO₂ gives the benzoprefulvene biradical 6 . The latter in its singlet state undergoes ring closure to 1 , or it opens to give naphthalene.     

Stoichiometric and catalytic reductive aldol cyclizations of alkynediones induced by Stryker's reagent

Conjugate reduction of alkynones by stoichiometric [(Ph(3)P)CuH](6) or catalytic [(Ph(3)P)CuH](6) and polymethyl-hydrosiloxane proceeds to cyclization by an aldol reaction with tethered ketones to generate [small beta]-hydroxyenones with good diastereoselectivity.