Asymmetric synthesis of beta-amino carbonyl compounds with N-sulfinyl beta-amino Weinreb amides

[reaction: see text] Diverse organometallic reagents readily add to enantiopure N-sulfinyl beta-amino Weinreb amides providing the corresponding, stable, N-sulfinyl beta-amino carbonyl compounds in good to excellent yields. This new methodology represents a general solution to the problem of beta-amino carbonyl syntheses, which are important chiral building blocks and constituents of natural products. N-Sulfinyl beta-amino Weinreb amides are prepared by reaction of the potassium enolate of N-methoxy N-methylacetamide with sulfinimines (N-sulfinyl imines) or lithium N,O-dimethylhydroxylamine with N-sulfinyl beta-amino esters.     

N-sulfinyl beta-amino Weinreb amides: synthesis of enantiopure beta-amino carbonyl compounds. Asymmetric synthesis of (+)-sedridine and (-)-allosedridine

[reaction: see text] N-Sulfinyl beta-amino Weinreb amides are prepared by condensation of sulfinimines with the potassium enolate of N-methoxy-N-methylacetamide. These new chiral building blocks are useful for the asymmetric synthesis of beta-amino carbonyl compounds, as illustrated here by the concise enantioselective syntheses of sedum alkaloids (+)-sedridine and (-)-allosedridine.     

The discretized flow on domains of attraction: a structural stability result

It is well known that, for stepsize sufficiently small, compactattractors of ordinary differential equations persist underdiscretization. The present paper describes the structure ofthe discrete-time dynamical system obtained via discretizationon A(M_h)\M_h where M_h is the approximate attractor and A(M_h)is its domain of attraction. The existence of a smooth embeddinginto a continuous-time parallelizable flow is proved. The constructioncan be used to define sections for discretizations and can beinterpreted as a justification of the method of modified equations.     

Controlled derivatization of polyhalogenated quinolines utilizing selective cross-coupling reactions

Straightforward procedures for the derivatization of tri- and tetrahalogenated quinolines utilizing sequential selective Pd-catalyzed cross-coupling reactions are described. Taking advantage of intrinsic halide reactivity, substrate control, and appropriate reaction conditions, highly selective reactions at the quinoline 3-, 4-, and 6-position are possible.     

Convenient preparation of substituted 5-aminooxazoles via a microwave-assisted Cornforth rearrangement

The preparation of oxazole-4-carboxamides and their subsequent thermal rearrangement to 5-aminooxazole-4-carboxylates is optimized in a high-speed microwave-assisted procedure. The reaction sequence is effective with a variety of substituted oxazoles, and produces products in good yield and high purity.     

Asymmetric synthesis of acyclic 1,3-amino alcohols by reduction of N-sulfinyl beta-amino ketones. Formal synthesis of (-)-pinidinol and (+)- epipinidinol

Stereoselective reduction of acyclic N-sulfinyl beta-amino ketones with (LiEt(3)BH) and Li(t-BuO)(3)AlH, respectively, gave anti- and syn-1,3-amino alcohols with excellent selectivity. A formal asymmetric synthesis of the hydroxy piperidine alkaloids (-)-pinidinol and (+)-epipinidinol from a common N-sulfinyl beta-amino ketone ketal precursor was developed. The pinidinol piperidine ring was formed via a novel acid-catalyzed cascade reaction of a N-sulfinylamino silyl protected alcohol ketal.     

Detection of atomic oxygen and further line assignments in the far-infrared stratospheric spectrum

The analysis of the high resolution far infrared emission spectrum of the stratosphere has made possible the identification of two features due to atomic oxygen. Several other new features have been assigned on the basis of updated line compilations. The possible detection of HBr, HO₂ and H₂O₂ in the far infrared is discussed.     

Cosmic-ray backgrounds in infrared bolometers

Cosmic-ray events are produced in infrared detectors by energy impulses which result from the ionization trails of fast charged particles. Model calculations are compared to the pulse-amplitude spectrum observed in a balloon flight from Palestine, Texas, at an altitude of 38 km. The results are useful for understanding cosmic-ray backgrounds which occur in all applications of high sensitivity bolometers.