Concepcion C. Gonzalez

Fragmentation of Carbohydrate Anomeric Alkoxy Radicals: A New Synthesis of Chiral 1-Halo-1-iodo Compounds

One less carbon atom is found in 1-halo-1-iodo compounds obtained by C1-C2 radical fragmentation of carbohydrate 1,2-halohydrins. This fragmentation is achieved via the anomeric alkoxy radicals of the halohydrins, formed upon reaction with (diacetoxyiodo)benzene and iodine [Eq. (1); X=Cl, Br, I].

Chemoselective Intramolecular Functionalization of Methyl Groups in Nonconstrained Molecules Promoted by N-Iodosulfonamides

Mechanistic evidence observed in Hofmann-Löffler-Freytag-type reactions has been crucial to achieve the chemoselective functionalization of methyl groups under mild conditions. Radical-mediated methyl iodination and subsequent oxidative deiodination are the key steps in this functionalization, where iodine chemistry has a pivotal role on the formation of the C-N bond. The concepts of single hydrogen atom transfer (SHAT) and multiple hydrogen atom transfer (MHAT) are introduced to describe the observed chemoselectivity.

A mild oxidative decarboxylation of carbohydrate acids

Abstract The oxidative decarboxylation of carbohydrate uronic or ulosonic acids with simultaneous replacement by an acetoxy group has been accomplished using the (diacetoxyiodo)benzene and iodine system under mild conditions. A general synthesis of derivatives of tetrodialdoses, and pentodialdoses in furanose or pyranose form is described.

Fragmentation of carbohydrate anomeric alkoxy radicals. A new synthesis of alduronic acid lactones

Abstract Aldopyranosuronic and aldofuranosuronic acid lactones, with one carbon less, can be specifically obtained when hexuronic and penturonic acids in pyranose or furanose forms undergo a tandem β-fragmentation-cyclization reaction promoted by the system (diacetoxyiodo)benzene-iodine, under mild conditions. The lactones are formed via 1,5 and 1,6 intramolecular cyclization.

Fragmentation of Carbohydrate Anomeric Alkoxyl Radicals: New Synthesis of Chiral 1‐Fluoro‐1‐halo‐1‐iodoalditols

A new general methodology for the synthesis of 1,1,1-trihaloalditols by starting from 1,5-anhydro-2-deoxy-hex-1-enitol derivatives (glycals) is described. The halogens are introduced sequentially in each of the three different steps of the process. The fluorine is introduced in the first step by electrophilic fluorination of the starting glycal; next, hydroxyhalogenation of the resulting vinyl fluoride allows the addition of any halogen (F, Cl, Br or I) at will, and finally, an iodine atom is inserted through an alkoxyl radical fragmentation reaction. This methodology allows the preparation of diverse types of 1,1,1-trihalogenated compounds (R--CF(2)I, R--CFI(2), R--CFClI and R--CFBrI) under mild conditions compatible with sensitive substituents. In some cases, the diastereomeric mixtures generated from R--CFClI and R--CFBrI can be chromatographically separated, and their configuration determined by X-ray crystallographic analysis. The synthetic usefulness of these compounds has been preliminarily assessed by examining the reactivity of the fluorinated radical generated by rupture of the C--I bond.

Fragmentation of carbohydrate anomeric alkoxy radicals: a new synthesis of chiral 1-halo-1-bromo compounds

The reaction of 1,2-halohydrins derived from easily available carbohydrates with (diacetoxyiodo)benzene (DIB) in the presence of bromine is a mild procedure for the synthesis of 1-deoxy-1-halo-1-bromo-alditols with one carbon less than the original carbohydrate. The reaction goes through β-fragmentation of the intermediate anomeric alkoxyl radicals. These 1-halo-1-bromo polyhydroxy compounds may be valuable synthetic intermediates in organic synthesis.

Synthesis of Tetrazole-Fused Glycosides by a Tandem Fragmentation–Cyclization Reaction

The fragmentation of anomeric alkoxyl radicals (ARF) and the subsequent intramolecular cyclization promoted by hypervalent iodine reagents provide an excellent method for the synthesis of tetrazolo-sugars. This new reaction offers additional advantages for the synthesis of these compounds, including the ready availability of the starting materials, experimental simplicity, mild conditions, and good yields.

Fragmentation of carbohydrate anomeric alkoxy radicals. Synthesis of azasugars

Abstract The reaction of conveniently protected 5-amino-5-deoxy pentoses and 6-amino-6-deoxy hexoses with iodosylbenzene and iodine is an efficient method, via β-fragmentation of the anomeric alkoxy radicals, for the synthesis of azasugars of the tetrose and pentose series, respectively.

Synthesis of phenanthridones, quinolinequinones and 7-azasteroids

Abstract Cleavage of ring D of lycorines, obtained by an intramolecular cycloaddition of an aryne to an azadiene, led to phenanthridines, which were either oxidized to quinolinequinones or cyclized to 7-azasteroids, both of which families are of potential pharmacological interest.

A new intramolecular aryne cycloaddition approach to lycorines

Abstract A new approach to lycorines based on the intramolecular cycloaddition of an azadiene and an aryne is reported. The azadiene component was formed by the double bond of an imine and a double bond belonging to an aromatic ring, and the aryne was generated by dehydrohalogenation of an aryl bromide with LDA.