The formation and stereoselective quenching of 1-mannopyranosyl radicals by a tributyltin hydride-mediated intramolecular 1,5-hydrogen abstraction sequence is described. A competing process is 1,4-hydrogen atom abstraction leading principally to glucopyran-2-ulosides. Fragmentation of the anomeric radical resulting in the formation of ring opened products is a problem in certain series. The chemistry is dictated to a considerable extent by the nature of the protecting groups employed with the 4,6-benzylidene series and, for rhamnose, the Ley 3,4-dispiroketal, being particularly susceptible to the 1,4-hydrogen atom abstraction but less to the fragmentation. Photochemical conditions are described, in which these side reactions are practically eliminated, and applied to the inversion of an alpha- to a beta-mannoside in a disaccharide.

To study the dynamics and mechanism of intramolecular photoinduced electron transfer (PET) reactions, a series of (Zn II -Fe III ) meso-tetraarylmetalloporphyrin dimers were synthesized and the kinetics of their PET reactivity was measured. Molecular building blocks were prepared by selective nucleophilic aromatic substitution of a para fluorine on tetraarylporphyrins containing a single pentafluorophenyl group. This synthetic approach allows a wide variety of systematic modifications such as type and length of spacer, metal center, and redox-potential difference between donor and acceptor. The edge-to-edge distance between the two porphyrins varies from 14.4 to 27.3 Å. Into a symmetric dimer, with two identical porphyrins covalently linked by a rigid partly saturated bridge, one zinc(II) and one iron(III) can be inserted. From measurements of fluorescence lifetimes the rate constants for PET from the electronically excited state of the zinc porphyrin to the bis(imidazole)iron porphyrin cation were evaluated. The electron-transfer rate decreases by a factor of only 165 when the distance increases by 13 Å. This small decrease is indicative of a surprisingly weak attenuation of the electronic coupling with distance.

A method for the in situ formation of N-trifluoroacetoxy succinimide (TFA-NHS) and its application in the formation of succinimidyl esters is presented. The developed method provides N-trifluoroacetyl and N-maleoyl amino acid succinimidyl esters from a variety of amino acids using a one-pot, high-yielding protocol. Investigations into the formation of an N-maleoyl amino acid succinimidyl ester supported the proposal of a revised reaction mechanism, and contributed to the optimization of the reaction conditions.