Stereoselective formation of quaternary stereogenic centers via alkylation of α-substituted malonate-imidazolidinones

A new stereoselective alkylation methodology is presented for formation of chiral, nonracemic quaternary centers via a chiral auxiliary protocol involving α-alkylated malonate imidazolidinones. Based on two X-ray structures of quaternized products, the diastereoselectivity observed may be rationalized via a transition-state involving an s-transC-N conformation of the C-N bond of the auxiliary, with the metal cation (K(+)) chelated into the malonate six-membered hole as a Z-enolate. A deprotection protocol involving ethanethiolate exchange of the imide to the corresponding thioester, followed by a standard Fukuyama reduction and a borohydride reduction, furnishes α,α'-quaternized β-hydroxypropionates in high ee overall.

An alternative stereoselective synthesis of (R)- and (S)-Rosaphen® via asymmetric catalytic hydrogenation

We report an alternative synthesis of the two enantiomers of the floral fragrance Rosaphen®. The key intermediate 2-methyl-5-phenylpentanoic acid 3 is synthesized via asymmetric hydrogenation (ee up to 99%) in the presence of an in situ prepared ruthenium catalyst containing the chiral ferrocenyl phosphine Mandyphos-4.

Enantioselective synthesis of the female sex pheromone of the pink hibiscus Mealybug, Maconellicoccus hirsutus

The pink hibiscus mealybug, Maconellicoccus hirsutus (Green), is an exotic insect pest and recently invaded Southern California and Florida. The female M. hirsutus releases the 2-methylbutanoate of a novel cyclobutanoid monoterpene alcohol (maconelliol) that together with lavandulyl 2-methylbutanoate constitutes the sex pheromone to attract males from a distance. Enantioselective syntheses of four different stereoisomers of the major component, maconelliyl 2-methylbutanoate 1, from alpha-pinene are reported. Absolute configurations of both naturally occurring maconelliyl 2-methylbutanoate 1 and the minor component, lavandulyl 2-methylbutanoate 2, have been established. Comparison of the analytical data of naturally occurring compounds with those of optically active synthetic isomers proved that both esters show the (R)-configuration at the alcohol and the (S)-configuration at acid moieties.