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Monday, March 26, 2012
Douglass F. Taber
University of Delaware

Reactions of Alkenes: The RajanBabu Synthesis of Pseudopterosin G-J Aglycone Dimethyl Ether

Xiangge Zhou of Sichuan University showed (Tetrahedron Lett. 2011, 52, 318. ) that even the monosubstituted alkene 1 was smoothly converted to the methyl ether 2 by catalytic FeCl3. Brian C. Goess of Furman University protected (J. Org. Chem. 2011, 76, 4132. ) the more reactive alkene of 3 as the 9-BBN adduct, allowing selective reduction of the less reactive alkene, to give, after reoxidation, the monoreduced 4. Nobukazu Taniguchi of the Fukushima Medical University added (Synlett 2011, 1308. ) Na p-toluenesulfinate oxidatively to 1 to give the sulfone 5. Krishnacharya G. Akamanchi of the Institute of Chemical Technology Mumbai oxidized (Synlett 2011, 81. ) 1 directly to the bromo ketone 6.

Osmium is used catalytically both to effect dihydroxylation, to prepare 8, and to mediate oxidative cleavage, as in the conversion of 7 to the dialdehyde 9. Ken-ichi Fujita of AIST Tsukuba devised (Tetrahedron Lett. 2011, 52, 3137. ) magnetically retrievable osmium nanoparticles that can be re-used repeatedly for the dihydroxylation. B. Moon Kim of Seoul National University established (Tetrahedron Lett. 2011, 52, 1363. ) an extraction scheme that allowed the catalytic Os to be re-used repeatedly for the oxidative cleavage.

Maurizio Taddei of the UniversitÓ di Siena showed (Synlett 2011, 199. ) that aqueous formaldehyde could be used in place of Co/H2 (syngas) for the formylation of 1 to 10. Hirohisa Ohmiya and Masaya Sawamura of Hokkaido University prepared (Org. Lett. 2011, 13, 1086. ) carboxylic acids (not illustrated) from alkenes using CO2. Joseph M. Ready of the UT Southwestern Medical Center selectively arylated (Angew. Chem. Int. Ed. 2011, 50, 2111. ) the homoallylic alcohol 11, to give 12.

Many reactions of alkenes are initiated by hydroboration, then conversion of the resulting alkyl borane. Hiroyuki Kusama of the Tokyo Institute of Technology photolyzed (J. Am. Chem. Soc. 2011, 133, 3716. ) 14 with 13 to give the ketone 15. William G. Ogilvie of the University of Ottawa added (Synlett 2011, 1113. ) the 9-BBN adduct from 1 to 16 to give 17. Professors Ohmiya and Sawamura effected (Org. Lett. 2011, 13, 482. ) a similar conjugate addition, not illustrated, of 9-BBN adducts to α,β-unsaturated acyl imidazoles.

Melanie S. Sanford of the University of Michigan used (Org. Lett. 2011, 13, 1076. ) Pd catalysis to oxidize 18 to the arylated acetate 20. Ilhyong Ryu of Osaka Prefecture University also used (Org. Lett. 2011, 13, 2114. ) Pd catalysis to effect the branching homologation of 1 to the diester 22.

T. V. RajanBabu of the Ohio State University set (J. Am. Chem. Soc. 2011, 133, 5776. ) the stereogenic center of 24 by asymmetric hydrovinylation of 23, using ethylene. Two more of the four stereogenic centers were set by asymmetric hydrovinylation in the course of the synthesis of Pseusopterosin G-J Aglycone Dimethyl Ether (25).

D. F. Taber, Org. Chem. Highlights 2012, March 26.