Synthesis of chiral phosphino-sulfoximines through phospha-Michael addition and their evaluation as 1,5-P,N-Ligand in asymmetric allylic alkylation

Despite the availability of several classes of P,N-ligands, there is still a quest for this new type of ligands for many catalytic applications. This work describe the synthesis of new phosphino-sulfoximines and their application as 1,5-P,N-ligand in palladium-catalyzed asymmetric allylic alkylation. The key step of the synthesis of phosphino-sulfoximines is the introduction of the phosphorus via a phospha-Michael addition with enantiomerically pure vinyl sulfoximines using diphenylphosphine and a catalytic amount of potassium tert-butoxide. The resulting phosphines were in situ treated with borane to prevent oxidation at the phosphorous atom and the corresponding phosphine boranes were isolated in good yields with low to moderate diastereoselectivities. Treatment of the phosphine boranes with DABCO afforded the corresponding phosphino-sulfoximines in excellent yields. The phosphino-sulfoximines were tested as ligand in palladium-catalyzed allylic alkylation of rac-(E)-1,3-diphenyl-2-propenyl acetate with dimethyl malonate. The corresponding malonate was obtained with enantiomeric excess (ee) up to 89%. Moreover, the following conclusions were drawn: 1) A matched and mismatched configuration of the ligand was observed. 2) The ee of the corresponding malonate decreased at high Ligand:Metal ratio (L:M), which is probably due to a monodentate P-coordination mode of the ligand at L:M>1. In order to induce a higher degree of enantiocontrol, the sulfoximine and the phosphino group were embedded into a cyclohexyl ring which would confine the flexibility of the backbone to favour a bidentate coordination mode. Cyclic phosphino-sulfoximines were synthesized using the same strategy, i.e. phospha-Michael addition of cyclic vinyl sulfoximines. Two new stereogenic centres were created, and over four expected isomers, only both trans isomers of the phosphines were formed. Using the cyclic phosphino-sulfoximines as ligand, ee up to 97% were obtained. The following conclusions were drawn: 1) The L:M ratio has no influence on the catalytic course. 2) There is a matched and mismatched configuration of the ligand. 3) NMR analysis of the pi-allyl-palladium complex bearing the most efficient ligand confirmed the bidentate P,N coordination mode of the cyclic phosphino-sulfoximine.

Grantor dc:publisher

Publikationsserver der RWTH Aachen University

Year dc:date

2008

Author dc:creator

• Lemasson, Fabien

Contributors dc:contributor

• Gais, Hans-Joachim

• info:eu-repo/classification/ddc/540
• Sulfoximin
• Homogene Katalyse
• Allylierung
• Zweizähniger Ligand
• Michael-Addition
• Chemie
• asymmetrische Katalyse
• Phospha-Michael-Addition
• P,N-Ligand
• palladium Katalyse
• asymmetric catalysis
• chiral P,N-ligand
• sulfoximine
• phospha Michael addition
• allylic substitution

Statement dc:rights

• info:eu-repo/semantics/openAccess

Language dc:language

eng

Identifier

https://publications.rwth-aachen.de/search?p=id:%22RWTH-CONV-112892%22

OAI record oai:identifier

https://publications.rwth-aachen.de/oai2d?verb=GetRecord&metadataPrefix=oai_dc&identifier=oai%3Apublications.rwth-aachen.de%3A50343