A stereoselective N-iminium ion cyclization with allylsilane to construct vicinal quaternary-tertiary carbon centers was developed for the concise synthesis of (±)-cephalotaxine. The current strategy features a TiCl4-promoted cyclization and ring-closure metathesis to furnish the spiro-ring system. The stereochemical outcome in the N-acyliminium ion cyclization was rationalized by the stereoele...

Silica ferric hydrogensulfate is an efficient heterogeneous catalyst for the cyclization of 2- aminochalcones to the corresponding 2,3-dihydroquinolin- 4(1H)-ones. This intramolecular aza Michael reaction was carried out in high yields using chalcones bearing of electron donating and electron withdrawing groups. The catalyst is reusable without significant decreases in its activity after four t...

the method cited in the literature for synthesis of 1,2- dihydro 3- thioxo - 1,2,4- benzotriazine 1 was improved .1 was condensed with propargyl bromide to afford 3 - propargylthio – 1,2,4 -benzotriazine 5. transformation of this compound to 9h-3- methylthiazolo [2,3-c] [1,2,4] benzotriazine ( 3, r = me) was performed in the presence of na o me / meoh . orientation of this selective cyclization...

A series of [b]-fused 6,7-diethynylquinoxaline derivatives have been synthesized through an imine condensation strategy to examine the effect of extended benzannelation on the thermal reactivity of enediynes. Absorption and emission spectra of the highly conjugated quinoxalenediynes were red-shifted approximately 100-200 nm relative to those of 1,2-diethynylbenzene. Strong exotherms indicative ...

Cloutier and Widom [Cloutier, T. E. & Widom, J. (2004) Mol. Cell 14, 355-362] recently reported that the cyclization efficiency of short DNA fragments, about 100 bp in length, exceeds theoretical expectations by three orders of magnitude. In an effort to resolve this discrepancy, we tried modifying the theory. We investigated how the distribution of the angles between adjacent base pairs of the...

Capillary Gas Chromatography (CGC) is capable of determining underivatized cyclophosphamide (CPA) using SCOT OV 275 columns. Then CPA is subjected to in situ degradation resulting in formation of a cyclization product which can be determined selectively in biological fluids. In routine bioanalysis however cyclization products of CPA metabolites might interfere, e.g. 4-keto CPA. In the present s...

Straightforward access to [1,2]-annulated indoles, key substructures in natural products, is highly desirable yet challenging. Herein, a radical triggered fragmentary cyclization cascade reaction of ene-ynamides presented, providing rapid into indoles by an intermolecular addition, intramolecular cyclization, desulfonylative aryl migration, and site-selective C(sp2)-N sequence. DFT calculations...

An efficient cyclization of 2’-hydroxychalcone to flavanone using calcium chloride as a catalyst was developed. The scope of the reaction was studied with substituted 2’-hydroxychalcone and these chalcones was converted into corresponding flavanone in good yield. The merits of this method are inexpensive and easily available catalyst, easy workup procedure, avoid use of toxic solvent

Cyclization and annulation reactions initiated by ring-opening of small rings, especially cyclopropanes and cyclobutanes are now well-established in synthetic chemistry. Nevertheless, the potential of aminocyclopropanes and cyclobutanes, an important subclass for the synthesis of nitrogen-rich building blocks, has remained unexploited for a long time, despite important pioneering results. In th...