Reactions of the natural lignan hydroxymatairesinol in basic and acidic nucleophilic media: formation and reactivity of a quinone methide intermediate

The chemical properties and synthetic modifications of the natural lignan hydroxymatairesinol in basic and acidic nucleophilic media were studied. Hydroxymatairesinol presumably reacts via a quinone methide and a carbonium ion mechanism under basic and acidic conditions, respectively. In these conditions the benzylic hydroxyl group was displaced by nucleophiles yielding new 7-substituted butyrolactone lignans. Reactions in alcoholic basic solutions yielded the 7-alkoxy ethers diastereoselectively. Several previously known lignans as well as new lignans and lignan derivatives were synthesised. The transformations were monitored and the products identified by HPLC-MS and NMR.     

Real forms of complex higher spin field equations and new exact solutions

We formulate four-dimensional higher spin gauge theories in spacetimes with signature (4−p,p)$(4-p,p)$ and non-vanishing cosmological constant. Among them are chiral models in Euclidean (4,0)$(4,0)$ and Kleinian (2,2)$(2,2)$ signature involving half-flat gauge fields. Apart from the maximally symmetric solutions, including de Sitter spacetime, we find: (a) SO(4−p,p)$\mathit{SO}(4-p,p)$ invariant deformations, depending on one continuous and infinitely many discrete parameters, including a degenerate metric of rank one; (b) non-maximally symmetric solutions with vanishing Weyl tensors and higher spin gauge fields, that differ from the maximally symmetric solutions in the auxiliary field sector; and (c) solutions of the chiral models furnishing higher spin generalizations of type D gravitational instantons, with an infinite tower of Weyl tensors proportional to totally symmetric products of two principal spinors. These are apparently the first exact 4D solutions with non-vanishing massless higher spin fields.     

Photo-redox induced cationic polymerization of divinyl ethers

The cationic polymerization of diethyleneglycoldivinyl ether was initiated by cationic species originating from the redox reaction between photochemically generated free radicals or excited state photosensitizers and various onium salts. For the oxidation of free radicals, the efficiency of the initiation process depended primarily on the redox potential of the redox couple and hence the reactivity could be altered by choosing an appropriate combination of free radical photoinitiator and onium salt. The electron transfer from excited state photosensitizers to the phenacyletramethylenesulfonium salt showed no correlation between the free energy of the process and the initiation efficiency.