Roche ester

Abstract: Asymmetric hydrogenations of monoenes and dienes were performed to obtain terminal deoxypolyketide fragments A and the corresponding internal chirons B and C. The chiral N-heterocyclic carbene catalyst 1 was used throughout. Modest selectivities for hydrogenations of simple monoenes relayed into high selectivities for preparations of the terminal deoxypolyketide fragments in which either two hydrogenations or one and an optically pure starting material were used. Curiously, the face selectivities for hydrogenation of alpha,beta-unsaturated esters were consistently opposite to those that had been observed for styrene and stilbene derivatives in previous work, and to closely related allylic alcohol and ether derivatives in this work. Plausible mechanisms for this differing behavior were deduced by using DFT calculations. It appears that the origin of the unusual stereoselectivity for the ester derivatives is transient metal-coordination of the ester carbonyl whereas there is no evidence that the allylic alcohol or ethers coordinate. The routes developed to alpha,omega-functionalized internal deoxypolyketide fragments are extremely practical. These begin with the Roche ester being converted into alkene and, in one case, diene derivatives. Catalyst control prevails in the hydrogenations of these substrates, but there is a significant "substrate vector" (a term we used to describe the influence of the substrate on a catalyst-controlled reaction). This is determined by minimization of 1,3-allylic strain and, in some cases, syn pentane interactions. This substrate vector can be constructively paired with the (dominant) catalyst vector by use of the appropriate enantiomer of 1. In the hydrogenation of a diene derivative, two chiral centers could be formed simultaneously with overall 11:1.0 selectivity; this is the first time this has been achieved in any asymmetric synthesis of a deoxypolyketide fragment. Throughout, diastereoselectivities of the crude material in the syntheses of alpha,omega-functionalized internal deoxypolyketide fragments were in excess of 11:1.0 and chromatographically purified samples could be isolated in high yields with dr (dr=diastereomeric ratio) values consistently in excess of 40:1.0.

Abstract: A new class of ferrocenyl chiral bisphosphorus ligand, Wudaphos, was developed, and exhibits excellent ee and activity (ee up to 99%, TON up to 20 000) for the asymmetric hydrogenation of both 2-aryl and 2-alkyl acrylic acids through ion pair noncovalent interaction under base free and mild reaction conditions. Well-known anti-inflammatory drugs such as naproxen and ibuprofen together with the intermediate for the preparation of Roche ester and some bioactive compounds were also efficiently obtained with excellent ee. Control experiments were conducted and revealed that the ion pair noncovalent interaction and chain length played important roles.

Abstract: Roche ester derivatives were converted to trisubstituted alkenes with allylic chiral centers. Hydrogenation of these substrates with chiral analogues of Crabtree’s catalyst, specifically, an optically active carbene oxazoline derivative, were found to be mostly catalyst controlled. However, the peripheral functionalities and protecting groups had significant effects and could be adjusted to give high stereoselectivities. The upshot of this work is that α,ω-functionalized chirons to introduce 1,2-dimethyl functionalities into acyclic chains have been developed.

Abstract: (S)-3-Hydroxy-2-methylpropionate, known as the Roche ester, and several of its derivatives were successfully synthesized through asymmetric rhodium-catalyzed hydrogenation, using INDOLPHOS (diisopropyl{1-[(S)-3,5-dioxa-4-phosphacyclohepta[2,1-a;3,4-a]dinaphthalen-4-yl]-3-methyl-2-indolyl}phosphine) as the chiral ligand, in excellent yield and the highest ee reported up to now (TOF over 5500 h-1 at 25 °C; up to 98% ee at -40 °C).