Starting from santonin,the total syntheses of cytotoxic monomeric,dimeric and trimeric quainolides dehydrozalu...
Yong Qin West China School of Pharmacy,Sichuan University,Chengdu 610041 P.R.China Innovative Drug Research Centre,Chongqing University,Chongqing 401331,P.R.China
Starting from the oxygenated piperidine building block 20,two synthetic approaches to new building blocks (8R,8aS)-and (8R,8aR)-8-hydroxy-5-indolizidinones 19a/19b and 15a/15b have been developed,respectively. The first one is based on the trans-diastereoselective reductive alkylation (dr = 93:7),followed by a four-step procedure; and the second one called for the RCM reaction on the N,O-acetal derived from a vinylation,which was followed by a pyrrole formation,and a stereocontrolled cis-selective (dr = 91:9) catalytic hydrogenation. Reduction of the diastereomer 15a produced (8R,8aR)-8-indolizidinol (18).
The intermolecular Pauson-Khand reaction between 2-ethynylbenzaldehyde and ethylene promoted by dimethyl sulfide can be utilized to synthesize 2-（2-formylphenyl）cyclopentenone efficiently. This compound and its deriva- tives undergo a cascade process of Michael addition reaction followed by Henry reaction with nitromethane to con- struct substituted aromatic fused 2,3-dihydroindanones. Furthermore, direct one-pot synthesis of aromatic fused 2,3-dihydroindanones from 2-ethynylbenzaldehyde is achieved.
Some Stemona alkaloids belonging to the tuberostemospironine group possess a spirolactone moiety with anti-configuration （C-9/C-9a）. In this paper, we describe two approaches to this structural unity. By using bromine atom as a traceless directing group, the SmI2-mediated reductive coupling of ketone 6 and fl-bromomethacrylate proceeded with complete anti-diastereoselectivity. In the absence of an a-directing （chelation） group, the one-pot reaction of the ketone derived from alcohol 15 with the organozinc reagent generated from bromomethacrylate af- forded spiro-a-methylene-y-lactone derivative 16 as a single diastereomer. These two highly diastereoselective methods would find application in the synthesis of stemona alkaloids containing anti-configured spiro-lactone/pyr- rolidine moieties. In addition, on the basis of our previous work, the total synthesis of （-）-9-epi-11-demethyl- sessilifoliamide J （11）, and an improved synthesis of （-）-9,11-di-epi-sessilifoliamide J （9） were accomplished.
＜正＞The oxidative Heck reaction via direct C-H activation has gain tremendous interests during the past decades...
Peng Li~1,Gang Zhao~*,Shizheng Zhu~* Key Laboratory of Organofluorine Chemistry,Shanghai Institute of Organic Chemistry,The Chinese Academy of Sciences,345Lingling Road,Shanghai 200032,P.R.China
A novel strategy was developed for a rapid access to the naturally occurring racemic neoclausenamide and its analogs, which featured a highly erythro-selective vinylogous Mukaiyama type reaction （dr= 12：1） and a highly diastereoselective tandem conjugate addition-Davis oxidation ofN-Boc-pyrrol-2（5H）-one 5 （dr= 10：1）. Remarka- bly, the skeleton of neoclausenamide, namely 8n, an analog of neoclausenamide, was built in just two steps with all the four stereogenic centers （relative stereochemistry） established correctly and in excellent diastereoselectivities.
