Direct Zn-diamine promoted reduction of C=O and C=N bonds by polymethylhydrosiloxane in methanol

Ketones and imines are chemoselectively reduced at room temperature in methanol to the corresponding alcohols and amines in high yields in a one-step procedure using polymethylhydrosiloxane (PMHS) and a simple zinc-diamine catalyst.     

A theory of the J/gY→η(η′)γ decays

It is argued that the $\text{J}\text{gY}\text{→η(η′)γ}$ decay rates are directly calculable within quantum chromodynamics. The calculation of $\text{Γ(}\text{J}\text{Ψ}\text{→ηγ)}$ is most straightforward and involves no new hypotheses as compared to, say, the $\text{J}\text{Ψ}\text{→}\text{e}{}^{\mathrm{+}}\text{e}{}^{\mathrm{?}}$ decay in detail earlier. To the contrary, evaluation of the $\text{J}\text{Ψ}\text{→η′γ}$ width puts on trial dynamical results concerning the η′ coupling to gluons. The latter depends crucially on non-perturbative power terms in the QCD sum rules. The calculated numbers for $\text{Γ(}\text{J}\text{Ψ}\text{→ηγ)}$ and $\text{Γ(}\text{J}\text{Ψ}\text{→η′γ)}$ agree well with the data.     

Use and misuse of QCD sum rules,factorization and related topics

The purpose of this paper is twofold. First, we are prompted by some recent publications to reply to the criticism of the QCD sum-rules approach contained therein. Hopefully, some of the discussion is of wider interest. In particular, we point out that the multi-gluon operators unlike the multi-quark ones, relevant to the sum rules, do not factorize at large N_c. This implies that the masterfield, even if it is found, will be of no immediate help in evaluating the quarkonium spectrum. Second, we derive new sum rules for light quarks which are sensitive to the mean intensity of the gluon field in the vacuum (the so-called gluon condensate, or 〈vac|G²|vac〉). New sum rules confirm the standard value of 〈vac|G²|vac〉. Some casual remarks on the π⁰ transitions into two virtual photons, π⁰ → γ^*γ^*, are also presented. Finally, we enumerate (in sect. 7) basic points of the sum-rule approach and discuss, im brief, the unsolved problems.     

Quantal problems with partial algebraization of the spectrum

We discuss a new class of spectral problems discovered recently which occupies an intermediate position between the exactly-solvable problems (e.g., harmonic oscillator) and all others. The problems belonging to this class are distinguished by the fact that a part of the eigenvalues, and eigenfunctions can be found algebraically, but not the whole spectrum. The reason explaining the existence of the quasi-exactly-solvable problems is a hidden dynamical symmetry present in the hamiltonian. For one-dimensional motion this hidden symmetry isSL(2,R). It is shown that other groups lead to a partial algebraization in multidimensional quantal problems. In particular,SL(2,R)×SL(2,R),SO(3) andSL(3,R) are relevant to two-dimensional motion inducing a class of quasi-exactly-solvable two-dimensional hamiltonians. Typically they correspond to systems in a curved space, but sometimes the curvature turns out to be zero. Graded algebras open the possibility of constructing quasi-exactlysolvable hamiltonians acting on multicomponent wave functions. For example, with a (non-minimal) superextension ofSL(2,R) we get a hamiltonian describing the motion of a spinor particle.     

Instantons in supersymmetric theories

Instanton effects are considered for a sample of supersymmetric theories, namely, quantum mechanics, gluodynamics, Higgs model. The problem is how to reconcile the apparent lack of the boson-fermion symmetry in the effective instanton induced interactions with supersymmetry of the corresponding lagrangians. It is shown that in the case of quantum mechanics and the Higgs model there is actually no conflict between supersymmetry and the instanton calculus since the Ward identities, associated with the supersymmetry transformations, are satisfied. In quantum mechanics this is due to spontaneous symmetry breaking, or pole terms in matrix elements of supercharge, while in the case of the supersymmetric Higgs model the effective fermion interaction just reduces to a total derivative. In the case of supersymmetric gluodynamics, however, the standard instanton calculus explicitly violates naive Ward identities.     

Total synthesis of (-)-colchicine via a Rh-triggered cycloaddition cascade

[reaction: see text] A synthesis of the antimitotic alkaloids (-)-colchicine and (-)-isocolchicine is reported. Important steps are (a) enantioselective transfer-hydrogenation of an alkynone, (b) iodine/magnesium exchange with subsequent aromatic acylation, (c) Rh-catalyzed transformation of an alpha-diazoketone into an oxatetracyclic key intermediate through intramolecular [3 + 2]-cycloaddition of an in situ generated carbonyl ylide, and (d) regioselective conversion of the cycloadduct into a tropolone derivative. The new synthetic strategy opens an efficient enantioselective access to colchicine and structural analogues.