Guanidines, cyclic

Amidines and cyclic amidines are also converted into 1,2,4-thiadiazoles by reaction with isothiocyanates, imino-sulfenyl chlorides, di- and trichloromethyl sulfenyl chlorides, and carbon disulfide in the presence of sulfur. Ureas, thioureas, guanidines, carbodiimides, and cyanimides react with chlorocarbonylsulfenyl chloride to produce 1,2,4-thiadiazol-5-one derivatives in another example of a type B synthesis <1996CHEC-II(4)307>. 

Six-membered cyclic guanidine 197 was transformed into the corresponding bicyclic guanidine hemiaminal after deprotection of the Cbz and contemporary cyclization on the masked aldehyde function (Equation 4). This product, 198, was then employed in a Biginelli reaction to form a precursor of alkaloid batzelladine F <1999JOC1512>. 

When the amine and the 5-alkylisothiouronium group are part of the same molecule, an intramolecular synthesis of a guanidine can occur with great ease [145, 146[. A special effect attributed to the presence of a cyclic system is the reaction between aziridines and 5-methylisothiouronium salts to give 2-methylthioethylguanidines [147, 215]. 

Scheme 16 Multicomponent synthesis of cyclic guanidine derivatives...

Lohmeijer BGG, Pratt RC, Leibfarth F, Logan JW, Long DA, Dove AP, Nederberg F, Choi J, Wade C, Waymouth RM, Hedrick JL (2006) Guanidine and amidine organocatalysis for ringopening polymerization of cyclic esters. Macromolecules 39 8574—8583... 

Tan also found that guanidine 21, acting as a base to activate the o [3], X [3] tautomers of diaryl phosphine oxides, catalyzes the asymmetric phospha-Michael reachon of aryl nitroalkenes (Scheme 5.42) [76]. He later employed 21 to realize highly enantioselective Michael additions of dithiomalonate and 3-keto thioesters with a range of acceptors, including maleimides, cyclic enones, furanone, and acyclic 1,4-dicarbonylbutenes [77]. 

The reaction works well when R and are alkyl or benzyl, or when NR R is a cyclic secondary amine. ° It also works with benzil and its para-substituted derivatives and with guanidine and its mono-substituted derivatives, giving high yields of products 35 having Ar = phenyl para-substituted with H, Cl, Me, and MeO, and R = R = R = H,... 

Reaction of 2-substituted 1,3-propanediamines 617 with carbon disulfide, followed by ring closure under micro-wave conditions gave 2-pyrimidinethiones 619, while reaction of the same diamines with cyanogen bromide in a one-pot microwave procedure gave cyclic guanidines 620 <2004JOC1571>. 

The power of cyclic chiral nitrones in synthesis was demonstrated by Nagasawa et al. (52) by the synthesis of the enantiomerically pure pentacyclic guanidine derivative 38 (Scheme 12.14). The 1,3-dipolar cycloaddition of 27b with 34 took... 

V,Af-Dimethylaniline A A,A, AT-Tetramethyl-p-phenylenediamine Cyclic amines 4,4 -Bipyridyl Quinoline Pyridine A-oxide Pyridinium chloride Hydroxides CsOH LiOH NaOH Triton B6 Alkylamines Ammonia Methylamine Ethylamine Propylamine Butylamine Decylamine Dodecylamine Tridecylamine Tetradecylamine Pentadecylamine Hexadecylamine Heptadecylamine Octadecylamine Tributylamine Miscellaneous Ammonium acetate Hydrazine Potassium formate Guanidine... 

Taylor and co-workers <99SL795> repotted some promising results with DBU-like cyclic guanidine derivatives of type 44, equipped with the appropriate chiral auxiliary. Both yields and ee s were modest, but the ready availability of the amine, and the flexibility of substitution on the... 

These compounds, cyclic derivatives of urea or guanidine, are as follows ... 

Note The following derivatives of ethylene guanidine apparently are capable of being isolated in the isomeric forms indicated, plus A(i) mino-or nitra (i) minoethyl guanidines (non-cyclic) not indicated, depending upon pH, thermal and temporal history of their method of prepn... 

Azirine derivatives 318 were shown in the same article to be precursors of triazines 324 (30-35% yield) and pyrimidines 326 (30% yield) upon treatment in DMSO with guanidine and formamidine, respectively (Scheme 71). A similar pathway to that outlined above is also invoked to explain these results thus, intermediate 323 would yield 324 by electro-cyclic ring closure, whereas 326 would be formed by heterocyclization of 325 and loss of ammonia (91JOC7). 

Thermal stability of a number of cyclic and acyclic nitramines, amine nitrate salts and guanidine derivatives [34]. 

In addition to the mechanism involving cyclic AMP, nonsugar sweeteners, eg, saccharin and a guanidine-type sweetener, have been found to enhance the production of another second messenger, inositol 1,4,5-trisphosphate (IP3), causing the closure of potassium channels and the release of... 

A quaternary ammonium hydroxide ion exchange resin 6 was shown to sequester phenols, hydroxypyrazoles, and other weakly acidic heterocycles.25 The sequestered nucleophiles could also be used as polymer-supported reactants. Similarly, the guanidine-functionalized resin 7 was also shown to be a useful capture agent for weakly acidic nucleophiles, including phenols and cyclic iV-acyl sulfonamides.26... 

Shieldings observed for the o- and p- N-phenyl ring carbons in cyclic guanidines are attributed to a ( + )-M electron releasing effect of the imino nitrogen. This indicates an N-phenylimino rather than the tautomeric N-phenylamino compound [348] (bottom of page 241). 

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