作者:Min Zheng、Ke Gao、Haitao Qin、Guigen Li、Hongjian Lu
DOI:10.1002/anie.202108617
日期:2021.10.11
enantiopurity of divergent products. Both reactions proceed efficiently with catalyst loading as low as 0.2 mol % and can be performed on a gram scale without loss of chemoselectivity or enantioselectivity. Chemodivergent asymmetric 1,5-aminocyanation or 1,5-oxocyanation of vinylcyclopropane can also be realized by this protocol. Mechanistic investigations involving electron paramagnetic resonance (EPR)
1,3-Dienes are readily available feedstocks that are widely used in the laboratory and industry. However, the potential of converting 1,3-dienes into value-added products, especially chiral products, has not yet been fully exploited. By synergetic photoredox/copper catalysis, we achieve the first visible-light-induced, enantioselective carbocyanation of 1,3-dienes by using carboxylic acid derivatives
New ring systems from 1,2-benzisothiazole-1,1-dioxides and related compounds
作者:Rudolph A Abramovitch、Ichiro Shinkai、B.J Mavunkel、K.M More、Sean O'Connor、Gino H Ooi、William T Pennington、P.C Srinivasan、James R Stowers
DOI:10.1016/0040-4020(95)01115-3
日期:1996.2
Ring-expansions and ring-annulations based on 3-substituted 1,2-benzisothiazole-1,1-dioxides have lead to a variety of novel heterocyclic systems. The reaction of 3-substituted (1H)-1-isoindolones with 1-diethylamino-1-propyne has also resulted in new, ring-expanded molecules in good to modest yields.
An improved process for the trimethylsilylation of organic compounds with at least one active hydrogen atom with hexamethyldisilazane, the improvement comprising effecting the reaction in the presence of 0.001 to 10 mole percent of a catalyst of the formula X--NH--Y I wherein X and Y are individually an electron-withdrawing group or when X is an electron-withdrawing group, Y is selected from the group consisting of hydrogen and trialkylsilyl of 1 to 6 carbon atoms or X and Y together with the nitrogen atom to which they are attached form a cyclic electron-withdrawing group and novel trimethylsilylated thiols of the formula ##STR1## wherein R is a 5-or 6-membered heterocycle having at least one nitrogen or sulfur heteroatom and optionally substituted with at least one member of the group consisting of alkyl of 1 to 6 carbon atoms, phenyl, trimethylsilyl, trimethylsilyloxycarbonylmethyl and alkylamino of 1 to 6 carbon atoms, and novel trimethylsilylated 3'-substituted cephalosporanic acid derivatives.
A new azetidine derivative of the formula: ##EQU1## wherein R.sub.1 represents a penicillin- or cephalosporin-amido group, R.sub.2 represents one of the groups of the following formulae: ##EQU2## wherein R.sub.4, R.sub.5 and R.sub.6 are the same or different and each represents a hydrogen atom or a lower alkyl or alkenyl group, n represents 2 or 3 and - in case formula IIB represents a phenyl group - this group may carry one to four further substituents selected from the group consisting of halogen atoms and lower alkyl, lower alkenyl and phenyl groups, R.sub.3 represents an amino group of the formula ##EQU3## wherein R.sub.7 represents a hydrogen atom or a lower alkyl group and R.sub.8 represents a lower alkyl group, or R.sub.3 represents a N,N'-disubstituted hydrazino group wherein the substituents are lower alkyl groups, e.g. the N,N'-diisopropylhydrazino group, or R.sub.3 represents the group --OR.sub.9, wherein R.sub.9 represents a hydrogen atom, a lower alkyl group, which group may be substituted by 1 to 3 halogen atoms or by 1 or 2 phenyl groups, werein the phenyl groups may be substituted by a methoxy or a nitro group, or R.sub.9 represents a phenacyl group or a salt-forming cation, And corresponding azetidine derivatives of formula I wherein the double bond in the propenyl side chain has been shifted from the 2- to the 1-position, which are versatile intermediates in the process of preparing cephalosporanic and penicillanic derivative.