Chiral thiazolidines in the enantioselective ethylation of aldehydes: An experimental and computational study

Publication date: Available online 1 October 2018Source: Journal of Organometallic ChemistryAuthor(s): Nélia C.T. Tavares, César T. Neves, Bruce F. Milne, Dina Murtinho, Alberto A.C.C. Pais, M. Elisa Silva SerraAbstractA library of new chiral thiazolidines was prepared starting from l-cysteine and d-penicillamine in a simple, short synthetic sequence. 2-Arylthiazolidines were obtained, as diastereoisomeric mixtures, with good yields and in short reaction times, through a new and greener procedure, using microwave irradiation. Their use as chiral ligands in the enantioselective ethylation of aromatic aldehydes was studied and optimized, originating good to excellent conversions and ee up to 94% in 6 h. A series of heteroaromatic and aliphatic substrates were also enantioselectively ethylated with success, with ee up to 77%. The distinct opposite chirality in l-cysteine and d-penicillamine makes the use of these ligands an interesting approach for obtaining both the (S) and (R) enantiomers of the chiral alcohols, compounds with potential applications in the area of fine chemistry. NMR studies were carried out using a diastereoisomeric mixture of thiazolidines, allowing the identification of the most stable structure. Computational studies confirmed this result and also gave important insight into the species involved in the catalytic cycle of the enantioselective alkylation.Graphical abstractd-Penicillamine and l-cysteine derived thiazolidines were obtained through a simple...

Source: Journal of Organometallic Chemistry - October 5, 2018 Category: Chemistry Source Type: research