Multicomponent Double Diels–Alder/Nazarov Tandem Cyclization of Symmetric Cross‐Conjugated Diynones to Generate [6‐5‐6] Tricyclic Products

The construction of complex polycyclic terpenoid products in an efficient and step‐economical manner using multicomponent and tandem processes is highly valuable. Herein, we report a tandem cyclization sequence that initiates with a multicomponent double Diels–Alder reaction of cross‐conjugated diynones, followed by a Nazarov cyclization to efficiently produce [6‐5‐6] tricyclic products with excellent regio‐ and diastereoselectivity. This methodology generates five new carbon–carbon bonds, three rings, quaternary or vicinal quaternary carbons, and stereogenic centers in a one‐pot reaction.     

Facile preparation of the individual diastereomers of thymidine 3′,5′-cyclic phosphorothioate (cTMPS)

A facile synthesis of the individual Sp and Rp 3,5-cyclic thymidine phosphorothioates is reported. The key intermediate is a methyl phosphite triester which is readily converted under free-radical conditions to the diastereomeric thiophosphates which are separated on SiO₂ and then cleanly dealkylated by $\text{t}$-BuNH₂, to the ami ne salts of title compounds.     

Spectrum of certain non-self-adjoint operators and solutions of Langevin equations with complex drift

As part of a program to evaluate expectations in complex distributions by longterm averages of solutions to Langevin equations with complex dirft, a simple one-dimensional example is examined in some detail. The validity and rate of convergence of this scheme depends on the spectrum of an associated non-selfadjoint Hamiltonian which is found numerically. In the regime where the stochastic evaluation should be accurate numerical solution of the Langevin equation shows this to be the case.     

O2AIBN,free-radical method for the stereospecific oxidation of nucleoside trialkyl phosphites: new preparation of the individual,diastereomeric, 18O-labeled thymidine 3′, 5′-cyclic monophosphates.

An experimentally easy method for reqio- and stereospecific introduction of isotopic ¹⁸O or ¹⁷O) oxygen into phosphorus di- and triesters of biological interest is described and applied to ¹⁸O-labelinq of cTMP's.     

Two-Dimensional Turbulence with Rigid Circular Walls

We report numerical computations of decaying two-dimensional Navier--Stokes turbulence inside a circular rigid boundary. We summarize previously reported calculations involving no-slip boundary conditions and present results with higher spatial resolution than achieved before (with, however, no qualitative changes in the observed behavior). We then report new results with stress-free boundary conditions (for a viscous fluid, but bounded by a perfectly slippery wall). The method used is spectral, involving expansions of the fields in orthonormal sets of functions which obey two boundary conditions (circular analogues of the Chandrasekhar–Reid functions). The computation takes place entirely in the spectral space. Large-scale Reynolds numbers are typically less than a thousand. Interest focuses on the role played by angular momentum, in determining the decay of the turbulence with no-slip boundary conditions, and the role of possible other ideal invariants in the stress-free case. Received 30 September 1996 and accepted 5 February 1997     

Oneway Sagnac device to measure absolute velocity

The difference in the intensity of light produced by two independent beams passing in opposite directions through a oneway Sagnac device may be used to measure the absolute velocity of the device and, thus, the solar system.     

A study of the spectra and acidity of 4,5-dihydro-1H-benz[g]indazol-7-ol and 2,3a,4,5-tetrahydro-7-hydroxy-3a-methyl-3H-benz[g]indazol-3-one

The synthesis of 2,3a,4,5-tetrahydro-7-hydroxy-3H-benz[g]indazol-3-one is recorded for the first time. Infrared, pmr, and uv spectral analysis of this pyrazolone and of 4,5-dihydro-1H-benz[g]indazol-7-ol strongly support the presence of one tautomer in each case. Measurements of pK_a values are in agreement with the proposed tautomeric structures based upon comparisons with simpler model systems. The data are taken in aqueous solution since the compounds are soluble at 10^?5 M and the results may more closely approximate that for the structure under physiological conditions.     

An automatic apparatus for simultaneous thermograv- imetric and magnetic susceptibility measurements

An apparatus is described which records automatically the continuous sample mass-change curve, the apparent mass-changes caused by the magnetic field, and the sample temperature, all simultaneously over the temperature range from room temperature to 500°. The use of the apparatus is illustrated by the thermal dissociation of [Co(NH₃)₆]Cl₃. Data obtained from the apparatus permit the plotting of mass-change, mass susceptibility, and molar percent reduction of cobalt(III) curves, all as a function of temperature. Such information is useful in elucidating the mechanism of the thermal dissociation reaction.