Diastereotopos-differentiating C-H activation reactions at methylene groups.

The activation of C-H bonds has become a widely used method which allows for the direct transformation of C-H bonds into synthetically more valuable C-C and C-X bonds in a selective manner. This critical review aims to summarize and to highlight a specific subgroup of these transformations, C-H activation reactions of chiral substrates bearing diastereotopic hydrogen atoms at methylene groups (95 references).

Acyclic stereocontrol in the catalytic C-H amination of benzylic methylene groups.

Diastereotopos-differentiation is the key feature of the catalytic C-H amination at the benzylic position of substrate 1. Essentially independent of the functional group X (X = COOMe, PO(OEt)(2), SO(2)Ph, NO(2), CN, OAc), the depicted products 2 are formed with good (dr = 80/20) to excellent (dr > 95/5) diastereoselectivity. The reaction proceeds without racemization and possesses potential for the C-H amination of open-chain substrates.

Formal total synthesis of (+/-)-estrone and zirconocene-promoted cyclization of 2-fluoro-1,7-octadienes and ru-catalyzed ring closing metathesis.

A new and diastereoselective method for the synthesis of the estrone skeleton from a substituted styrene based on sequential 3-fold use of Cp 2ZrBu 2 (oxidative addition-alkylation and two cyclization-alkylation sequences) and a ruthenium complex catalyzed RC-metathesis of a sterically hindered diene was developed. The prepared estratetraene was obtained in 7 steps from a commercially available starting material and thus the overall synthesis of estrone could be accomplished in 9 steps. Moreover, we have also found that the course of the reaction of substrates bearing the 2-halo-1,7-diene moiety with Cp 2ZrBu 2, i.

Synthesis of (+/-)-3-Methoxyestra-1,3,5(10)-trienes by the repetitive use of Negishi reagent.

[reaction: see text] The repetitive use of Cp(2)ZrBu(2) (Negishi reagent) was applied in the synthesis of three 3-methoxyestra-1,3,5(10)-trienone isomers within four steps from the advanced intermediate 11. The overall synthesis is based on three zirconium-mediated reactions: (a) oxidative addition of a benzyl ether, (b) cyclization of an allyl-ene compound, and (c) cyclocarbonylation of a diene. The presented synthesis demonstrates that complex organic compounds can be prepared by the repetitive use of one reagent.

New Lewis-basic N-oxides as chiral organocatalysts in asymmetric allylation of aldehydes.

Allylation of aromatic and heteroaromatic aldehydes 1a-k with allyltrichlorosilane 2 can be catalyzed by the new heterobidentate, terpene-derived bipyridine N-monoxides 4, 6a,b, and 8-11 ( View Article and Find Full Text PDF