Ring Closure Reactions of Substituted 4-Pentenyl-1-oxy Radicals. The Stereoselective Synthesis of Functionalized Disubstituted Tetrahydrofurans
摘要:
N-(Alkyloxy)pyridine-2( VT)-thiones 3 and benzenesulfenic acid O-esters 5 have been synthesized from substituted 4-pentenols 1 or the derived tosylates. Compounds 3 and 5 are efficient sources of free alkoxy radicals 6 which undergo synthetically useful fast ring closure reactions 6 --> 8 [k(exo) = (2 +/- 1) x 10(8) s(-1) to (6 +/- 2) x 10(9) s(-1) (T = 30 +/- 0.2 degrees C)]. Tetrahydrofurfuryl radicals 8 can be trapped with, e.g., hydrogen or chlorine atom donors to afford either trans- or cis-disubstituted tetrahydrofurans 10 or 12 depending on the substitution pattern of the 4-pentenyloxy radical. Substituted tetrahydropyrans 11 or 13 are formed in the minor 6-endo-trig cyclization. According to the data of competition kinetics, the observed stereoselectivities in free alkoxy radical cyclizations arise from steric interactions between the substituents in the transition state of the ring closure reactions. Alkyl substituents cause small differences in the measured relative rate constants of B-exo cyclizations which are reminiscent of the data obtained from the rearrangements of alkyl-substituted 5-hexenyl radicals. Likewise, a stereochemical model for oxygen radical cyclization is proposed where the pentenyloxy chain adopts a six-membered, chairlike transition state with the alkyl substituents preferentially situated in the pseudoequatorial positions leading to 2,5-trans-, 2,4-cis-, and 2,3-trans-substituted tetrahydrofurfuryl radicals 8 as the major intermediates.
complex presented higher reactivity in the transferhydrogenation (TH) of ketones in 2-propanol. Experimentally, it was established that both the benzimidazole and amine N–H proton played a vital role in the enhancement of the catalytic activity. Utilizing this system a wide range of aldehydes and ketones were reduced efficiently. Notably, the TH of several imines, as well as chemoselective reduction of
6,6′-Dihydroxy terpyridine: a proton-responsive bifunctional ligand and its application in catalytic transfer hydrogenation of ketones
作者:Cameron M. Moore、Nathaniel K. Szymczak
DOI:10.1039/c2cc36927c
日期:——
The ligand 6,6â²-dihydroxy terpyridine (dhtp) is presented as a bifunctional ligand capable of directing proton transfer events with metal-coordinated substrates. Solid-state analysis of a Ru(II)-dhtp complex reveals directed hydrogen-bonding interactions of the hydroxyl groups of dhtp with a Ru-bound chloride ligand. The utility of dhtp was demonstrated by chemoselective transfer hydrogenation of ketones.
METHOD FOR PRODUCING OLEFINICALLY UNSATURATED CARBONYL COMPOUNDS BY OXIDATIVE DEHYDROGENATION OF ALCOHOLS
申请人:Limbach Michael
公开号:US20110004025A1
公开(公告)日:2011-01-06
A process for preparing olefinically unsaturated carbonyl compounds by oxidative dehydrogenation in an oxygenous atmosphere over a supported catalyst which comprises gold and optionally further noble metals at temperatures in the range from 50 to 240° C.
Compounds capable of activating cholinergic receptors
申请人:——
公开号:US20030125345A1
公开(公告)日:2003-07-03
The present invention generally relates to nicotinic compounds, in the form of aryl substituted olefinic compounds, as well as pro-drug, N-oxide, metabolite and pharmaceutically acceptable salt forms thereof. Methods of modulating neurotransmitter release via administration of the compounds, pro-drugs, N-oxides and/or pharmaceutically acceptable salts are also disclosed.
5-(Methylthio)tetrazoles as versatile synthons in the stereoselective synthesis of polycyclic pyrazolines via photoinduced intramolecular nitrile imine–alkene 1,3-dipolar cycloaddition
作者:Daniel Pla、Derek S. Tan、David Y. Gin
DOI:10.1039/c4sc00107a
日期:——
A key thioether substituent in readily accessible 2-alkyl-5-(methylthio)tetrazoles enables facile photoinduced denitrogenation and intramolecularnitrileimine 1,3-dipolar cycloaddition to afford a wide range of polycyclic pyrazoline products with excellent diastereoselectivity. The methylthio group red-shifts the UV absorbance of the tetrazole, obviating the requirement in all previous substrate systems