In Situ Protecting Groups for Chemoselective Transformations

2021 ◽  
pp. 327-372
Author(s):  
Alan Steven
Keyword(s):  
Protecting Groups

The AA* + B*B2 approach A simple and convenient synthetic strategy towards hyperbranched polyurea-urethanes

e-Polymers ◽  
2003 ◽  
Vol 3 (1) ◽  
Author(s):  
Bernd Bruchmann ◽  
Wolfgang Schrepp
Keyword(s):  
Functional Groups ◽  
Raw Materials ◽  
Protecting Groups ◽  
Isophorone Diisocyanate ◽  
Step Process ◽  
Synthetic Strategy ◽  
One Step

Abstract Synthesizing hyperbranched polyurethanes in a one step process using commercially available raw materials: these were the primary conditions for this work. By taking advantage of intramolecular reactivity differences of isocyanate groups in diisocyanates in combination with reactivity differences of OH and NH groups in alkanolamines, it is possible to generate in situ AB2 molecules by controlling reactions of specific functional groups towards each other. This AA* + B*B2 approach works without protecting groups and opens up a simple and versatile strategy towards hyperbranched aromatic as well as aliphatic polyureaurethanes. Preferential diisocyanates for this synthesis were 2,4-toluylene diisocyanate and isophorone diisocyanate, whereas diethanolamine and diisopropanolamine were used as isocyanate-reactive counterparts.

Selective Synthesis of exo-Spiro[2′,2′-difluorocyclopropane-3′,2′-tropanes]

Synthesis ◽  
2020 ◽  
Vol 52 (07) ◽  
pp. 1015-1024
Author(s):  
Andrii Gerasov ◽  
Grygoriy A. Dolgonos ◽  
Aleksandr Yu. Mandzhulo ◽  
Alexey Ryabitsky ◽  
Volodymyr Fetyukhin ◽  
...  
Keyword(s):  
Activation Barrier ◽  
Protecting Groups ◽  
Selective Synthesis ◽  
Double Bonds ◽  
Lower Activation ◽  
Conformationally Restrained

Conformationally restrained exo-isomers of N-Boc-protected spiro[2′,2′-difluorocyclopropane-3′,2′-tropanes] were synthesized in 62–83% yield via absolutely diastereoselective cycloaddition of CF2, generated in situ from Me3SiCF3/NaI in refluxing THF, to double bonds of 3-alkylidenetropanes. Standard removal of Boc protecting groups afforded corresponding exo-spiro[2′,2′-difluorocyclopropane-3′,2′-tropane] hydrochlorides in 82–94% yields. DFT and CCSD(T) calculations revealed that the observed exo-selectivity of difluorocarbene addition is likely to be caused by a lower activation barrier of the exo-difluorocyclopropanation compared to the endo-reaction.

Synthesis and Biological Effects of Acyclic Analogs of Deazapurine Nucleosides

1993 ◽  
Vol 58 (3) ◽  
pp. 629-648 ◽  
Author(s):  
Hana Dvořáková ◽  
Antonín Holý ◽  
Ivan Votruba ◽  
Milena Masojídková
Keyword(s):  
Biological Activity ◽  
Acid Hydrolysis ◽  
Acid Medium ◽  
Biological Effects ◽  
Protecting Groups ◽  
Diethyl Acetal ◽  
Subsequent Removal ◽  
Antiviral Activities ◽  
Cesium Salts

Deaza analogs of three basic types of S-adenosyl-L-homocysteine hydrolase (SAHase) inhibitors, (S)-DHPA (I), eritadenine (II) and AHPA (III), were prepared. Alkylation of 3-deazaadenine (V), 3-deazapurine (VI), 1-deazaadenine (VII) and 4-amino-6-bromo-5-cyanopyrrolo[2,3-d]pyrimidine (XXII) with (R)-2,2-dimethyl-4-tosyloxymethyl-1,3-dioxolane (XIIIb), followed by acid hydrolysis, afforded the corresponding (S)-2,3-dihydroxypropyl derivatives XVIIa -XIXa and XXV. Reaction of V and VII with 2,3-O-cyclohexylidene-D-erythrono lactone (XXIX) and subsequent removal of the protecting groups in an acid medium gave eritadenine analogs XXVII and XXVIII. Compounds V and VII were alkylated with bromoacetaldehyde diethyl acetal to give N-(2,2-diethoxyethyl) derivatives XXXII and XXXIII from which the substituted acetaldehyde derivatives were liberated in situ and converted into compounds XXX and XXXI by cyanohydrine reaction followed by acid hydrolysis. The alkylations were performed in dimethylformamide with sodium or cesium salts of the bases. Biological activity was observed only with 3-deazaadenine derivatives XVIIa, XXVII and XXX, which exhibit both enzyme-inhibitory and antiviral activities.

scholarly journals Photo-Removable Protecting Groups for in Situ DNA Microarray Synthesis

2004 ◽  
Vol 50 (10) ◽  
pp. 1936-1939 ◽  
Author(s):  
Farhana Afroz ◽  
Anthony D Barone ◽  
Paul A Bury ◽  
Chuan Chen ◽  
Andrea Cuppoletti ◽  
...  
Keyword(s):  
Dna Microarray ◽  
Protecting Groups

The use of immobilized crown ethers as in-situ N-protecting groups in organic synthesis and their application under continuous flow

Tetrahedron ◽  
2009 ◽  
Vol 65 (8) ◽  
pp. 1618-1629 ◽  
Author(s):  
Gareth. P. Wild ◽  
Charlotte Wiles ◽  
Paul Watts ◽  
Stephen J. Haswell
Keyword(s):  
Organic Synthesis ◽  
Crown Ethers ◽  
Continuous Flow ◽  
Protecting Groups

Rendez vous with Saturn's rings

1984 ◽  
Vol 75 ◽  
pp. 743-759 ◽  
Author(s):  
Kerry T. Nock
Keyword(s):  
Solar Energy ◽  
Electric Propulsion ◽  
Power Source ◽  
Propulsion System ◽  
Low Thrust ◽  
Ring Plane ◽  
The Earth ◽  
Total Impulse ◽  
Saturn's Rings

ABSTRACTA mission to rendezvous with the rings of Saturn is studied with regard to science rationale and instrumentation and engineering feasibility and design. Future detailedin situexploration of the rings of Saturn will require spacecraft systems with enormous propulsive capability. NASA is currently studying the critical technologies for just such a system, called Nuclear Electric Propulsion (NEP). Electric propulsion is the only technology which can effectively provide the required total impulse for this demanding mission. Furthermore, the power source must be nuclear because the solar energy reaching Saturn is only 1% of that at the Earth. An important aspect of this mission is the ability of the low thrust propulsion system to continuously boost the spacecraft above the ring plane as it spirals in toward Saturn, thus enabling scientific measurements of ring particles from only a few kilometers.

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