Bismuth compounds in organic synthesis. A one-pot synthesis of homoallyl ethers and homoallyl acetates from aldehydes catalyzed by bismuth triflate

[reaction: see text] Three one-pot methods for the conversion of aldehydes to homoallyl ethers catalyzed by Bi(OTf)(3).xH(2)O (1 < x < 4) have been developed. The one-pot synthesis of homoallyl ethers can be achieved either by in situ generation of the acetal followed by its reaction with allyltrialkylsilane or by a three-component synthesis in which the aldehyde, trimethylorthoformate or an alkoxytrimethylsilane and allyltrimethylsilane are mixed together in the presence of bismuth triflate (0.1-1.0 mol %). In addition, a three-component synthesis of homoallyl acetates, which is achieved by reacting the aldehyde, acetic anhydride, and allyltrimethylsilane in the presence of bismuth triflate (3.0-5.0 mol %), has been developed. The use of a relatively nontoxic, easy to handle, and inexpensive catalyst adds to the versatility of these methods.     

Complete (1)H and (13)C assignments of the four major saponins from Dioscorea villosa (wild yam)

Complete (1)H and (13)C spectral assignments for the four major steroidal saponins isolated by methanolic extraction of the roots of Dioscorea villosa, collected in North Carolina, United States (in summer and autumn), are presented in this paper. The structures were determined by a combination of (1)H, (13)C and 2D NMR techniques and were found to be ((3beta,25R)-26-(beta-D-glucopyranosyloxy)-22-methoxyfurost-5-en-3-yl-O-beta-D-glucopyranosyl-(1 --> 3)-O-beta-D-glucopyranosyl-(1 --> 4)-O-[alpha-L-rhamnopyranosyl-(1 --> 2)]-beta-D-glucopyranoside (1) (or methyl parvifloside), ((3beta,25R)-26-(beta-D-glucopyranosyloxy)-22 methoxyfurost-5-en-3-yl-O-alpha-L-rhamnopyranosyl-(1 --> 2)-O-[beta-D-gluco- pyranosyl-(1 --> 4)]-beta-D-glucopyranoside (2) (or methyl protodeltonin), (3beta,25R)-spirost-5-en-3-yl-O-beta-D-glucopy ranosyl-(1 --> 3)-O-beta-D-glucopyranosyl-(1 --> 4)-O-[alpha-L-rhamnopyranosyl-(1 --> 2)]-beta-D-glucopyranoside (3) (or Zingiberensis saponin I) and (3beta,25R)-spirost-5-en-3-yl-O-alpha-L-rhamnopyranosyl-(1 --> 2)-O-[beta-Ds-glucopyranosyl -(1 --> 4)]-beta-D-glucopyranoside (4) (or deltonin).     

Benchmark studies of the BCRLM reactive scattering code: Implications for accurate quantum calculations

Summary The Bending Corrected Rotating Linear Model (BCRLM), developed by Hayes and Walker, is a simple approximation to the true multidimensional scattering problem for reactions of the type: A + BC AB + C. While the BCRLM method is simpler than methods designed to obtain accurate three-dimensional quantum scattering results, this turns out to be a major advantage in terms of our benchmarking studies. The computer code used to obtain BCRLM scattering results is written for the most part in standard FORTRAN and has been ported to several scalar, vector, and parallel architecture computers including the IBM 3090-600J, the Cray XMP and YMP, the Ardent Titan, IBM RISC System/6000, Convex C-1 and the MIPS 2000. Benchmark results will be reported for each of these machines with an emphasis on comparing the scalar, vector, and parallel performance for the standard code with minimum modifications. Detailed analysis of the mapping of the BCRLM approach onto both shared and distributed memory parallel architecture machines indicates the importance of introducing several key changes in the basic strategy and algorithms used to calculate scattering results. This analysis of the BCRLM approach provides some insights into optimal strategies for mapping three-dimensional quantum scattering methods, such as the Parker-Pack method, onto shared or distributed memory parallel computers.     

Collision-Induced dissociations of deprotonated peptides. Dipeptides containing aspartic or glutamic acids

Deprotonated dipeptides, on collisional activation, fragment by the characteristic process NH₂CH(R¹) CONHCH(R²)CO₂^? → NH₂^?C(R¹)CONHCH(R²)CO₂H → ^?NHCH(R²)CO₂H + NH₂C(R¹)?C?O, when R¹ and R² = H or alkyl. However, when one of the constituent amino acids is either aspartic acid or glutamic acid, the standard cleavage becomes minor in comparison with fragmentation through the α-side-chain of Asp or Glu. For example, [Asp-Leu - H]^? and [Leu-Asp - H]^? both fragment principally by loss of water, a fragmentation not normally noted for peptides. In addition, [Leu-Asp - H]^? loses CO₂ and also forms HO₂CCH?CHCO₂^?˙. These fragmentations establish that Asp is the C-terminal amino acid. In contrast, isomeric Glu dipeptides, e.g. [Glu-Ala - H]^? and [Ala-Glu - H]^? undergo similar fragmentation, both competitively losing H₂O and CO₂. Both spectra also contain a product ion at m/z 128, identified as the pyroglutamate anion. Product ion and deuterium-labelling studies have been used in an attempt to elucidate the complex fragmentation mechanisms in these systems.     

Gaussian Property of the Rings R(X) and R〈X〉

The content of a polynomial f over a commutative ring R is the ideal c(f) of R generated by the coefficients of f. A commutative ring R is said to be Gaussian if c(fg) = c(f)c(g) for every polynomials f and g in R[X]. A number of authors have formulated necessary and sufficient conditions for R(X) (respectively, R?X?) to be semihereditary, have weak global dimension at most one, be arithmetical, or be Prüfer. An open question raised by Glaz is to formulate necessary and sufficient conditions that R(X) (respectively, R?X?) have the Gaussian property. We give a necessary and sufficient condition for the rings R(X) and R?X? in terms of the ring R in case the square of the nilradical of R is zero.     

Would weighted-student funding enhance intra-district equity in Texas? A simulation using DEA

We use data envelopment analysis to model the educational production function, and then explore how a shift to weighted student funding using the student weights embedded in the Texas School Finance Formula would alter the allocation of inputs and potential outputs. School outputs are measured as value-added reading and math scores on standard achievement tests. We find that if school districts allocated their resources efficiently, then they would not allocate their resources to campuses according to the funding model weights. Policies that promote greater efficiency would also enhance equity in educational outcomes.     

The effect of a low-frequency sound source (acoustic thermometry of the ocean climate) on the diving behavior of juvenile northern elephant seals,Mirounga angustirostris

Changes in the diving behavior of individual free-ranging juvenile northern elephant seals, Mirounga angustirostris, exposed to the acoustic thermometry of the ocean climate (ATOC) sound source were examined using data loggers. Data loggers were attached to the animals and measured swim speed, maximum depth of dive, dive duration, surface interval, descent and ascent rate, and descent and ascent angle along with sound pressure level (SPL). The ATOC sound source was at a depth of 939 m and transmitted at 195 dB re: 1 microPa at 1 m centered at 75 Hz with a 37.5-Hz bandwidth. Sound pressure levels (SPL) measured at the seal during transmissions averaged 128 dB and ranged from 118 to 137 dB re: 1 microPa for the 60-90 Hz band, in comparison to ambient levels of 87-107 dB within this band. In no case did an animal end its dive or show any other obvious change in behavior upon exposure to the ATOC sound. Subtle changes in diving behavior were detected, however. During exposure, deviations in descent rate were greater than 1 s.d. of the control mean in 9 of 14 seals. Dive depth increased and descent velocity increased in three animals, ascent velocity decreased in two animals, ascent rate increased in one animal and decreased in another, and dive duration decreased in only one animal. There was a highly significant positive correlation between SPL and descent rate. The biological significance of these subtle changes is likely to be minimal. This is the first study to quantify behavioral responses of an animal underwater with simultaneous measurements of SPL of anthropogenic sounds recorded at the animal.