Reductive radical-initiated 1,2-C migration assisted by an azidyl group

We report here a novel reductive radical-polar crossover reaction that is a reductive radical-initiated 1,2-C migration of 2-azido allyl alcohols enabled by an azidyl group. The reaction tolerates diverse migrating groups, such as alkyl, alkenyl, and aryl groups, allowing access to n+1 ring expansion of small to large rings. The possibility of directly using propargyl alcohols in one-pot is also described. Mechanistic studies indicated that an azidyl group is a good leaving group and provides a driving force for the 1,2-C migration.

Spectroscopic identification of the phenyltelluryl radical and its reactivity toward molecular oxygen

The phenyltelluryl radical was prepared by high-vacuum flash pyrolysis of diphenyl ditelluride and was chacracterized by matrix isolation IR and UV/Vis spectroscopy. After doping the matrix with molecular oxygen and allowing bimolecular reactions, the hitherto unkown phenyltelluro peroxy radical formed and was identified via IR spectroscopy. Irradiation with light at λ = 436 nm leads to isomerization to the thermodynamically more stable novel phenyltelluroyl radical. All experimental findings agree well with density functional theory (UB3LYP/Def2QZVPP and UM06-2X/Def2QZVPP) computations.

Et3B-mediated two- and three-component coupling reactions via radical decarbonylation of α-alkoxyacyl tellurides: single-step construction of densely oxygenated carboskeletons

The single-step construction of various densely oxygenated carboskeletons was achieved by radical-based two- and three-component coupling reactions of sugar derivatives, without the need for light or heat. Et3B/O2-mediated decarbonylation readily converted α-alkoxyacyl tellurides to α-alkoxy carbon radicals, which intermolecularly added to glyoxylic oxime ether or enones to provide the two-component adducts. Furthermore, the three-component adducts were produced by an intermolecular aldol reaction between the aldehyde and the boron enolates generated by capture of the two-component radical intermediates by Et3B. This powerful coupling method serves as a novel strategy for the convergent synthesis of polyol natural products.

Combination of fluoroalkylation and Kornblum–DeLaMare reaction: a new strategy for the construction of (Z)-β-perfluoroalkyl enaminones

A novel strategy has been developed for the highly chemo- and stereo-selective synthesis of (Z)-β-perfluoroalkyl enaminones via a multicomponent radical reaction involving sequential fluoroalkylation and Kornblum–DeLaMare reaction.

Hydrotelluration of acetylenic esters: structural characterization of stereoisomers of methyl/ethyl β-(aryltelluro)acrylates

Synthesis of tellurated acrylates, ArTeCHCHCOOR and their solid state structures have been explored. The ¹²⁵Te chemical shift and ²J(¹H–¹²⁵Te) are useful indicators of their geometry in solution.

Cascade radical reaction of substrates with a carbon-carbon triple bond as a radical acceptor

The limitation of hydroxamate ester as a chiral Lewis acid coordination moiety was first shown in an intermolecular reaction involving a radical addition and sequential allylation processes. Next, the effect of hydroxamate ester was studied in the cascade addition–cyclization–trapping reaction of substrates with a carbon–carbon triple bond as a radical acceptor. When substrates with a methacryloyl moiety and a carbon–carbon triple bond as two polarity-different radical acceptors were employed, the cascade reaction proceeded effectively. A high level of enantioselectivity was also obtained by a proper combination of chiral Lewis acid and these substrates.

Enantioselective Radical Cyclizations: A New Approach to Stereocontrol of Cascade Reactions

Stereocontrol in a cascade radical addition-cyclization-trapping reaction was achieved by a new approach, which utilizes a hydroxamate ester moiety as a coordinating chiral Lewis acid tether between two radical acceptors. A remarkable feature of this reaction is the construction of three bonds and tertiary and quaternary stereogenic centers through both inter- and intramolecular carbon-carbon bond-forming processes. The chiral Lewis acid mediated reaction of oxime ethers also proceeded smoothly with good enantio- and diastereoselectivities, indicating the usefulness of the cascade approach for the asymmetric synthesis of various gamma-lactams.

Electrospray ionization mass spectrometric characterization of key Te(IV) cationic intermediates for the addition of TeCl4 to alkynes

Tellurium tetrachloride adds to alkynes via two pathways: a concerted syn-addition that yields Z-tri- and -tetrasubstituted alkenes or an anti-addition that yields E-alkenes. The mechanistic aspects of these divergent pathways for TeCl4 addition to alkynes have been investigated by on-line electrospray ionization (tandem) mass spectrometry (ESI-MS(/MS)). Via ESI-MS(/MS), we have been able to intercept and characterize the active electrophile TeCl3+ in tetrahydrofuran (THF) solutions of TeCl4, as well as its THF complex and several TeClx(OH)y+ derivatives. For the first time, also, key Te(IV) cationic intermediates of the electrophilic addition of TeCl4 to alkynes were captured for gas-phase MS investigation. The detailed structural data of cyclic tellurane intermediates intercepted herein seems to provide insights into the coordinative behavior of the Te(IV) atom and its mode of action towards biological targets.

Microwave-Assisted Group-Transfer Cyclization of Organotellurium Compounds

Primary- and secondary-alkyl aryl tellurides, prepared by arenetellurolate ring-opening of epoxides/ O-allylation, were found to undergo rapid (3-10 min) group-transfer cyclization to afford tetrahydrofuran derivatives in 60-74% yield when heated in a microwave cavity at 250 degrees C in ethylene glycol or at 180 degrees C in water. To go to completion, similar transformations had previously required extended photolysis in refluxing benzene containing a substantial amount of hexabutylditin. The only drawback of the microwave-assisted process was the loss in diastereoselectivity which is a consequence of the higher reaction temperature. Substitution in the Te-aryl moiety of the secondary-alkyl aryl tellurides (4-OMe, 4-H, 4-CF(3)) did not affect the outcome of the group-transfer reaction in ethylene glycol. However, at lower temperature, using water as a solvent, the CF(3) derivative failed to react. The microwave-assisted group-transfer cyclization was extended to benzylic but not to primary- and secondary-alkyl phenyl selenides.

Tailored synthesis of structurally defined polymers by organotellurium-mediated living radical polymerization (TERP): synthesis of poly(meth)acrylate derivatives and their di- and triblock copolymers

The organotellurium-mediated living radical polymerization (TERP) method allows the synthesis of various polyacrylate and polymethacrylate derivatives with precise control of molecular weight and with defined end groups. The method can be applied to the synthesis of AB-diblock and ABA- and ABC-triblock copolymers composed of different families of monomers.