The direct catalytic asymmetric aldol reaction

A Practical Synthesis of (rac)-Muscone and (R)-(–-)-muscone

A practical synthesis of ( rac)-muscone in three steps is described, using commercially available 1,10-dibromodecane as the starting material. In the first step, an aldol reaction of 1,10-dibromodecane with ethyl acetoacetate affords the important intermediate 2,15-hexadecanedione in 70% yield. A cyclisation reaction in the second step aided by propyl zinc iodide gives dehydro-muscone in 84% yield. Hydrogenation of dehydro-muscone with Pd–-C completes the synthesis of ( rac)-muscone. Furthermore, ( R)-(–-)-muscone is enantioselectively prepared via the formation of a ketal intermediate from dehydro-muscone and 1,4-di- O-benzyl- D-threitol.

Direct enantioselective aldol-Tishchenko reaction catalyzed by chiral lithium diphenylbinaphtholate

Chiral lithium diphenylbinaphtholate is an effective catalyst for the enantioselective aldol-Tishchenko reaction, affording 1,3-diol derivatives with three contiguous chiral centers and high stereoselectivities. Successive aldol-aldol-Tishchenko reactions gave a triol derivative with five consecutive chiral centers. The present reaction was applicable to highly enantioselective Evans-Tishchenko reduction.

Highly stereoselective and scalable anti-aldol reactions using N-(p-dodecylphenylsulfonyl)-2-pyrrolidinecarboxamide: scope and origins of stereoselectivities

A highly enantio- and diastereoselective anti-aldol process (up to >99% ee, >99:1 dr) catalyzed by a proline mimetic-N-(p-dodecylphenylsulfonyl)-2-pyrrolidinecarboxamide-has been developed. Catalyst loading as low as 2 mol % can be employed. Use of industry-friendly solvents for this transformation as well as neat reaction conditions have been demonstrated. The scope of this transformation on a range of aldehydes and ketones is explored. Density functional theory computations reveal that the origins of enhanced diastereoselectivity are due to the presence of nonclassical hydrogen bonds between the sulfonamide, the electrophile, and the catalyst enamine that favor the major anti-Re aldol TS in the Houk-List model.