Monday, March 18, 2013
Tristan H. Lambert
Reactions of Alkenes
Paul J. Chirik at Princeton University reported (Science 2012, 335, 567. ) an iron catalyst that hydrosilylates alkenes with anti-Markovnikov selectivity, as in the conversion of 1 to 2. A regioselective hydrocarbamoylation of terminal alkenes was developed (Chem. Lett. 2012, 41, 298. ) by Yoshiaki Nakao at Kyoto University and Tamejiro Hiyama at Chuo University, which allowed for the chemoselective conversion of diene 3 to amide 4. Gojko Lalic at the University of Washington reported (J. Am. Chem. Soc. 2012, 134, 6571. ) the conversion of terminal alkenes to tertiary amines, such as 5 to 6, with anti-Markovnikov selectivity by a sequence of hydroboration and copper-catalyzed amination. Related products such as 8 were prepared (Org. Lett. 2012, 14, 102. ) by Wenjun Wu at Northwest A&F University and Xumu Zhang at Rutgers via an isomerization-hydroaminomethylation of internal olefin 7.
Seunghoon Shin at Hanyang University (experimental work) and Zhi-Xiang Yu at Peking University (computational work) reported (J. Am. Chem. Soc. 2012, 134, 208. ) that 9 could be directly converted to bicyclic lactone 11 with propiolic acid 10 using gold catalysis. A nickel/Lewis acid multicatalytic system was found (Angew. Chem. Int. Ed. 2012, 51, 5679. ) by the team of Profs. Nakao and Hiyama to effect the addition of pyridones to alkenes, such as in the conversion of 12 to 13.
Radical-based functionalization of alkenes using photoredox catalysis was developed (J. Am. Chem. Soc. 2012, 134, 8875. ) by Corey R. J. Stephenson at Boston University, an example of which was the addition of bromodiethyl malonate across alkene 14 to furnish 15. Samir Z. Zard at Ecole Polytechnique reported (Org. Lett. 2012, 14, 1020. ) that the reaction of xanthate 17 with terminal alkene 16 led to the product 18. The radical-based addition of nucleophiles including azide to alkenes with Markovnikov selectivity (cf. 19 to 20) was reported (Org. Lett. 2012, 14, 1428. ) by Dale L. Boger at Scripps La Jolla using an Fe(III)/NaBH4 based system.
A remarkably efficient and selective catalyst 22 was found (J. Am. Chem. Soc. 2012, 134, 10357. ) by Douglas B. Grotjahn at San Diego State University for the single position isomerization of alkenes, which effected the transformation of 21 to 23 in only half an hour.
A highly efficient alkene hydrogenation catalyst SiliaCat Pd0, which consists of ultrasmall Pd(0) nanocrystallites in an organoceramic matrix, was shown (Org. Process Res. Dev. 2012, 16, 1230. ) by François Béland at SiliCycle and Mario Pagliaro at the Institute of Nanostructured Materials in Italy. This catalyst effected the quantitative hydrogenation of 24 with 0.1 mol% catalyst loading in only 2 h.
Ozonolysis of alkenes typically requires the destruction of ozonide intermediates by reductants such as triphenylphosphine or dimethylsulfide under procedures that require many hours. Patrick H. Dussault at the University of Nebraska at Lincoln showed (Org. Lett. 2012, 14, 2242. ) that pyridine catalyzed this process resulting in, for example, the production of 27 from 26 in 2-3 min without any additional reductive workup.
The generation of Grignard reagents with complex substrates is very challenging, a fact that has limited the use of organomagnesium compounds in late-stage synthetic operations. Bernhard Breit from the University of Freiburg found (Angew. Chem. Int. Ed. 2012, 51, 5730. ) that alkylmagnesium reagents can be readily obtained from alkenes by hydroboration followed by boron-magnesium exchange using a geminal dimagnesium reagent such as 30. One demonstration of the utility of this approach was provided by the conversion of styrene 28 to the Grignard 31, which was then coupled with 32 to produce alkene 33 with 93% ee.
T. H. Lambert, Org. Chem. Highlights 2013, March 18.