scholarly journals Enantioselective preparation of mechanically planar chiral rotaxanes by kinetic resolution strategy

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Ayumi Imayoshi ◽  
Bhatraju Vasantha Lakshmi ◽  
Yoshihiro Ueda ◽  
Tomoyuki Yoshimura ◽  
Aki Matayoshi ◽  
...  
Keyword(s):  
Asymmetric Synthesis ◽  
Organic Synthesis ◽  
Hydroxy Group ◽  
Kinetic Resolution ◽  
Maximum Yield ◽  
Chiral Auxiliary ◽  
The Other ◽  
Theoretical Maximum ◽  
Other Hand ◽  
Resolution Strategy

AbstractAsymmetric synthesis of mechanically planar chiral rotaxanes and topologically chiral catenanes has been a long-standing challenge in organic synthesis. Recently, an excellent strategy was developed based on diastereomeric synthesis of rotaxanes and catenanes with mechanical chirality followed by removal of the chiral auxiliary. On the other hand, its enantioselective approach has been quite limited. Here, we report enantioselective preparation of mechanically planar chiral rotaxanes by kinetic resolution of the racemates via remote asymmetric acylation of a hydroxy group in the axis component, which provides an unreacted enantiomer in up to >99.9% ee in 29% yield (the theoretical maximum yield of kinetic resolution of racemate is 50%). While the rotaxane molecules are expected to have conformational complexity, our original catalysts enabled to discriminate the mechanical chirality of the rotaxanes efficiently with the selectivity factors in up to 16.

scholarly journals Bifurcated synthesis of methylene-lactone- and methylene-lactam-fused spirolactams via electrophilic amide allylation of γ-phenylthio-functionalized γ-lactams

2020 ◽  
Vol 16 ◽  
pp. 2769-2775
Author(s):  
Tetsuya Sengoku ◽  
Koki Makino ◽  
Ayumi Iijima ◽  
Toshiyasu Inuzuka ◽  
Hidemi Yoda
Keyword(s):  
Hydroxy Group ◽  
The Other ◽  
Synthetic Methods ◽  
Other Hand ◽  
Acidic Conditions ◽  
High Yields

New synthetic methods for spirolactams bearing an α-methylene-γ-butyrolactone or its analogous methylene-lactam have been developed. The allylation of γ-phenylthio-functionalized γ-lactams with 2-(acetoxy)methyl acrylamides was accomplished by using 2.5 equivalents of NaH to give the corresponding adducts in excellent yields. The remaining phenylthio group was substituted with a hydroxy group by treatment with CuBr, and the resulting γ-hydroxyamides were cyclized under acidic conditions to afford the corresponding methylene-lactam-fused spirolactams in high yields. On the other hand, methylene-lactone-fused spirolactams could be delivered from the allyl adducts in high yields through a sequential N-Boc protection/desulfinative lactonization.

Copper-Catalyzed [3+2]/[3+2] Carboannulation of Dienynes and Arylsulfonyl Chlorides Enabled by Smiles Rearrangement: Access to Cyclopenta[a]indene-Fused Quinolinones

2021 ◽  
Author(s):  
Liwei Zhou ◽  
Xiaodong Liu ◽  
Haiyan Lu ◽  
Guobo Deng ◽  
Yun Liang ◽  
...  
Keyword(s):  
Transition Metal ◽  
Organic Synthesis ◽  
The Other ◽  
Cycloaddition Reactions ◽  
Smiles Rearrangement ◽  
Other Hand ◽  
Transition Metal Catalyzed ◽  
Carbocyclic Rings ◽  
Metal Catalyzed

On one hand, the construction of two fused five-membered carbocyclic rings remains an extremely challenging topic in organic synthesis. On the other hand, transition-metal-catalyzed dienynes cycloaddition reactions have become one...

Synthesis and transannular Diels–Alder reaction of a 13-membered macrocyclic triene having a tetrasubstituted enol ether as dienophile

1990 ◽  
Vol 68 (3) ◽  
pp. 404-411 ◽  
Author(s):  
Gervais Bérubé ◽  
Pierre Deslongchamps
Keyword(s):  
Organic Synthesis ◽  
Alder Reaction ◽  
Diels Alder ◽  
The Other ◽  
Enol Ether ◽  
Diels Alder Reaction ◽  
Other Hand ◽  
Tricyclic Compounds

The syntheses of the acyclic triene trans–trans–cis27 and trans–trans–trans31 are described. Macrocyclization and concomitant transannular Diels–Alder reaction were performed with the chloride derivative obtained from the trans–trans–cis triene alcohol 27 yielding a mixture of the tricyclic compounds trans–syn–trans33 and cis–syn–cis34. On the other hand, macrocyclization of the chloride derived from trans–trans–trans triene 31 was not successful. Keywords: transannular process, Diels–Alder reaction, macrocyclic triene, macrocyclization, tricyclic compounds, organic synthesis.

scholarly journals The effect on the percentage composition of the milk of (a) variations in the daily volume and (b) variations in the nature of the diet

1922 ◽  
Vol 12 (2) ◽  
pp. 111-124 ◽  
Author(s):  
William Taylor ◽  
Alfred D. Husband
Keyword(s):  
Maximum Yield ◽  
Point Of View ◽  
The Other ◽  
Milk Secretion ◽  
Percentage Composition ◽  
Other Hand ◽  
Butter Fat ◽  
Points Of View ◽  
Chief Interest ◽  
Stimulation Of

The study of lactation has almost always been undertaken from one of two very diverse points of view, the physiological and the commercial. The chief aim of the physiologist has been to determine, either the origin of the various constituents of the milk and the method of their elaboration, or the extent to which internal secretions affect the flow of milk by their initiation, inhibition or stimulation of milk secretion. From the commercial or agricultural point of view, on the other hand, the chief interest has centred round the problem of the production of butter fat, and a very large number of experiments have been conducted to determine by what method of feeding a cow could be caused to give the maximum yield of milk with the highest percentage of fat.

A study of cometary eruptions through OH radio-lines

1999 ◽  
Vol 173 ◽  
pp. 249-254
Author(s):  
A.M. Silva ◽  
R.D. Miró
Keyword(s):  
Short Duration ◽  
Growth Curves ◽  
The Other ◽  
Initial Mass ◽  
Radio Lines ◽  
Other Hand ◽  
Sudden Rise

AbstractWe have developed a model for theH2OandOHevolution in a comet outburst, assuming that together with the gas, a distribution of icy grains is ejected. With an initial mass of icy grains of 108kg released, theH2OandOHproductions are increased up to a factor two, and the growth curves change drastically in the first two days. The model is applied to eruptions detected in theOHradio monitorings and fits well with the slow variations in the flux. On the other hand, several events of short duration appear, consisting of a sudden rise ofOHflux, followed by a sudden decay on the second day. These apparent short bursts are frequently found as precursors of a more durable eruption. We suggest that both of them are part of a unique eruption, and that the sudden decay is due to collisions that de-excite theOHmaser, when it reaches the Cometopause region located at 1.35 × 105kmfrom the nucleus.

Closing the GAP—A 5Å Scanning Microscope

1969 ◽  
Vol 27 ◽  
pp. 6-7
Author(s):  
A. V. Crewe
Keyword(s):  
Normal Form ◽  
The Other ◽  
Resolving Power ◽  
Scanning Microscope ◽  
Conventional Microscope ◽  
Other Hand ◽  
Closing The Gap ◽  
Thermal Sources ◽  
Better Than ◽  
Transmission Microscope

We have become accustomed to differentiating between the scanning microscope and the conventional transmission microscope according to the resolving power which the two instruments offer. The conventional microscope is capable of a point resolution of a few angstroms and line resolutions of periodic objects of about 1Å. On the other hand, the scanning microscope, in its normal form, is not ordinarily capable of a point resolution better than 100Å. Upon examining reasons for the 100Å limitation, it becomes clear that this is based more on tradition than reason, and in particular, it is a condition imposed upon the microscope by adherence to thermal sources of electrons.

Life Beyond 1MeV

1980 ◽  
Vol 38 ◽  
pp. 30-33
Author(s):  
K.H. Westmacott
Keyword(s):  
Electron Microscopy ◽  
Past Experience ◽  
The Other ◽  
Good Case ◽  
Other Hand ◽  
The U.S

Life beyond 1MeV – like life after 40 – is not too different unless one takes advantage of past experience and is receptive to new opportunities. At first glance, the returns on performing electron microscopy at voltages greater than 1MeV diminish rather rapidly as the curves which describe the well-known advantages of HVEM often tend towards saturation. However, in a country with a significant HVEM capability, a good case can be made for investing in instruments with a range of maximum accelerating voltages. In this regard, the 1.5MeV KRATOS HVEM being installed in Berkeley will complement the other 650KeV, 1MeV, and 1.2MeV instruments currently operating in the U.S. One other consideration suggests that 1.5MeV is an optimum voltage machine – Its additional advantages may be purchased for not much more than a 1MeV instrument. On the other hand, the 3MeV HVEM's which seem to be operated at 2MeV maximum, are much more expensive.

Can the Academic Self-Concept be Positive and Realistic?

2005 ◽  
Vol 19 (3) ◽  
pp. 129-132 ◽  
Author(s):  
Reimer Kornmann
Keyword(s):  
Academic Performance ◽  
Opposite Effect ◽  
Self Esteem ◽  
Point Of View ◽  
The Other ◽  
Self Concept ◽  
High Ability ◽  
Self Image ◽  
Other Hand

Summary: My comment is basically restricted to the situation in which less-able students find themselves and refers only to literature in German. From this point of view I am basically able to confirm Marsh's results. It must, however, be said that with less-able pupils the opposite effect can be found: Levels of self-esteem in these pupils are raised, at least temporarily, by separate instruction, academic performance however drops; combined instruction, on the other hand, leads to improved academic performance, while levels of self-esteem drop. Apparently, the positive self-image of less-able pupils who receive separate instruction does not bring about the potential enhancement of academic performance one might expect from high-ability pupils receiving separate instruction. To resolve the dilemma, it is proposed that individual progress in learning be accentuated, and that comparisons with others be dispensed with. This fosters a self-image that can in equal measure be realistic and optimistic.

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