Enantioselective Synthesis of (R)‐Antofine and (R)‐Cryptopleurine

Abstract

Enantioselective syntheses of (R)-antofine and (R)-cryptopleurine starting from a 3-phenanthrenylpropanal derivative are reported. Asymmetric α-amination of this aldehyde is carried out in the presence of D-proline, which constitutes the key step in the syntheses and resulted in the formation of the new stereogenic center with very high enantioselectivity (94% ee).The indolizidine and quinolizidine moieties in the target molecules are formed through Pictet-Spengler reaction. The current method is shorter and high yielding in comparison with a similar strategy used for the synthesis of these molecules using proline-catalyzed α-hydroxylation of the same aldehyde.

Simulation and Testing of a Linear Array of Modified Four-Square Feed Antennas for the Tianlai Cylindrical Radio Telescope

“…The technique allows 100 m class telescopes such as Tianlai and the GBT, which only have angular resolution of several arc-minutes, to rapidly survey enormous comoving volumes at z ∼ 1 [1,17,27,31,37]. The overall promise of the intensity mapping technique has been studied by a number of authors [3,4,12,40,49].…”

Electrophilic Aminating Agents in Total Synthesis

“…In the context of total synthesis, azodicarboxylate aminating agents are by far the most popular electrophiles for the α‐amination of carbonyl compounds [69–77] . This is because they are commercially available, relatively bench stable, and highly electrophilic.…”

“…In the context of total synthesis,azodicarboxylate aminating agents are by far the most popular electrophiles for the aamination of carbonyl compounds. [69][70][71][72][73][74][75][76][77] This is because they are commercially available,relatively bench stable,and highly electrophilic.C hiral organocatalysts and chiral auxiliarybased methods have been developed that provide high enantioselectivities.F or the former,t he high efficiency of proline-based catalysts can be rationalized by the transition state indicated in Scheme 5; here,a pproach of the azodicarboxylate is directed by hydrogen bonding between one of its nitrogen centers and the carboxylic acid unit of the organocatalyst. This model is based on Houk and Listsc alculated transition state of the Hajos-Parrish-Eder-Sauer-Wiechert reaction, and is analogous to transition states that have been proposed for proline-catalyzed intermolecular Mannich and aldol reactions.…”

21 cm Signal Recovery via Robust Principal Component Analysis

“…Of course, in the most general case, there is an obvious degeneracy in the robust PCA problem Eq. (7) or its convex version -the PCP problem Eq. (8), i.e., how to distinguish L and S if both are sparse and have low ranks.…”

“…Observation of the neutral hydrogen (HI) distribution through its 21 cm line radiation can provide very precious information on the history of the Epoch of Reionization (EoR) [1][2][3][4] and the statistical properties of Large Scale Structure, which can be used to infer the nature of dark energy, dark matter, inflationary origin of the Universe [5][6][7][8][9]. Detecting the 21 cm signal in a cosmological experiment is a very challenging task, because there are various astrophysical foreground emissions, such as galactic synchrotron emission, free-free emission, recombination lines, and the extragalactic radio sources including quasars, radio galaxies and galaxy clusters, some of these are several orders of magnitude stronger than the 21 cm signal.…”