The stereochemistry of conjugate addition of lithium dialkyl cuprate reagents to some carbohydrate α-enones

Abstract

Conjugate addition-alkylation reactions of lithium dialkyl cuprates to hex-2-enopyrano-4-ulosides (1), hex-3-enopyrano-2-ulosides (2), and hex-1-enopyrano-3-uloses (3) have been investigated. Extensive studies with 1 show that the homogeneous system using the soluble tri-n-butylphosphine copper(I) complex is less satisfactory than the heterogeneous medium in which copper(I) iodide is used. The use of Grignard reagents versus alkyl lithiums has also been investigated, the latter being found preferable. 1,2-Addition was observed in some cases, but conditions were developed to avoid formation of these side products.With α-enones 1 and 2 alkylation is completely stereoselective, the newly introduced alkyl group being in axial orientation. With 3 a complex mixture is obtained from which equatorial and axial adducts can be isolated in approximately equal amounts.

Total Synthesis of Aryl C-Glycoside Natural Products: Strategies and Tactics

“…Reaction of 102 with higher-order phenylcuprate in the presence of acetic anhydride as trapping agent gave phenyl C -glycoside 103 in high yield (Scheme ). − In the absence of acetic anhydride, side reactions occurred, including epimerization at the C4-position and/or opening of the pyran ring.…”

Carbohydrate Derivatives in the Asymmetric Synthesis of Natural Products

“…Conjugate addition to (83b) gives (84) exclusively (106). However hydrogenation of the resulting methylene adduct proved to be less stereoselective than desired, giving a mixture of the C-4 epimers of (85).…”

“…Sorbitol (or D-glucitol) (106), an inexpensive, commercially available compound, is a dihydro derivative of D-glucose. Upon treatment with acid it forms the 1,4-anhydro system (107) in 36 percent yield.…”

Chemische Reaktionen und Derivatisierungen ungesättigter Zucker Teil 2

“…Weitere Beispiele fur diese Reaktionen finden sich in der Literatur [195]. Fraser-Reid und Mitarbeiter untersuchten die optimalen Bedingungen fur 1,4-Additionen an Enone rnit Lithiumdialkylkupferverbindungen [196]. Ebenfalls Fraser-Reid und Mitarbeiter untersuchten die photochemische Addition von Alkoholen [197] Es gelingt in der Regel, die beiden entstehenden Gleichgewichtspaarezu trennen.…”