Carbon-Carbon Bond Construction
Carlo Siciliano and Angelo Liguori of the Università della Calabria showed (J. Org. Chem. 2012, 77, 10575. ) that an amino acid 1 could be both protected and activated with FMOC-Cl, so subsequent exposure to diazomethane delivered the FMOC-protected diazo ketone 2. Pei-Qiang Huang of Xiamen University activated (Angew. Chem. Int. Ed. 2012, 51, 8314. ) a secondary amide 3 with triflic anhydride, then added an alkyl Grignard reagent with CeCl3 to give an intermediate that was reduced to the amine 4. John C. Walton of the University of St. Andrews found (J. Am. Chem. Soc. 2012, 134, 13580. ) that under irradiation, titania could effect the decarboxylation of an acid 5 to give the dimer 6. Jin Kun Cha of Wayne State University demonstrated (Angew. Chem. Int. Ed. 2012, 51, 9517. ) that a zinc homoenolate derived from 7 could be transmetalated, then coupled with an electrophile to give the alkylated product 8.
The Ramberg-Bäcklund reaction is an underdeveloped method for the construction of alkenes. Adrian L. Schwan of the University of Guelph showed (J. Org. Chem. 2012, 77, 10978. ) that 10 is a particularly effective brominating agent for this transformation. Daniel J. Weix of the University of Rochester coupled (J. Org. Chem. 2012, 77, 9989. ) the bromide 12 with the allylic carbonate 13 to give 14. The Julia-Kocienski coupling, illustrated by the addition of the anion of 16 to the aldehyde 15, has become a workhorse of organic synthesis. In general, this reaction is E selective. Jirí Pospísil of the University Catholique de Louvain demonstrated (J. Org. Chem. 2012, 77, 6358. ) that inclusion of a K+-sequestering agent switched the selectivity to Z. Yoichiro Kuninobu, now at the University of Tokyo, and Kazuhiko Takai of Okayama University constructed (Org. Lett. 2012, 14, 6116. ) the tetrasubstituted alkene 20 with high geometric control by the Re-catalyzed addition of 19 to the alkyne 18.
André B. Charette of the Université de Montréal converted (Org. Lett. 2012, 14, 5464. ) the allylic halide 21 to the alkyne 22 by displacement with iodoform followed by elimination. In an elegant extension of his studies with alkyl tosylhydrazones, Jianbo Wang of Peking University added (J. Am. Chem. Soc. 2012, 134, 5742. ) an alkyne 24 to 23 to give 25. This transformation may be proceeding by way of the diazo alkane. Xiaomin Cheng of Anhui University and Chaozhong Li of the Shanghai Institute of Organic Chemistry established (J. Am. Chem. Soc. 2012, 134, 14330. ) a complementary procedure, the decarboxylative coupling of an acid 26 with the reagent 27 to give the alkyne 25. For each of these protocols, it will be interesting to understand the diastereomeric preference in stereochemically defined systems. Matthias Tamm of the Technische Universität Braunschweig developed (Angew. Chem. Int. Ed. 2012, 51, 13019. ) a Mo metathesis catalyst that works with terminal alkynes such as 28.
Alexandre Alexakis of the University of Geneva coupled (Org. Lett. 2012, 14, 5880. ) a Grignard reagent 31 with the dichloride 30 to give the allene 32 in high ee. Regan J. Thomson of Northwestern University prepared (J. Am. Chem. Soc. 2012, 134, 5782. ) the aldehyde 33 by exposure of the acyclic dialdehyde to catalytic proline. Addition of 34 to the derived sulfonylhydrazone led, by way of the monoalkyl diazene, to the allene 35 with remarkable diastereocontrol.