A general, highly stereoselective synthesis of amines

Enantioselective imine reduction catalyzed by imine reductases and artificial metalloenzymes

Adding value to organic synthesis. Novel imine reductases enable the enantioselective reduction of imines to afford optically active amines. Likewise, novel bioinspired artificial metalloenzymes can perform the same reaction as well. Emerging proof-of-concepts are herein discussed.

Origin of pi-Facial Stereoselectivity in Nucleophilic Additions. Application of the Exterior Frontier Orbital Extension Model to Imines and Iminium Ions

The experimental data of pi-facial stereoselection of the imines and the iminium ions of cyclohexanone, tropinone, and adamantan-2-ones have been explained by the exterior frontier orbital extension model (EFOE model) previously proposed. In all cases, facial difference in the pi-plane-divided accessible space (PDAS), which represents simple summation of the pi-plane-divided exterior three-dimensional space nearest to the reaction center outside the van der Waals surface, significantly depends on the structure of the imino moieties. In particular the formation of iminium salt significantly affects the magnitude of both the EFOE density and the PDAS values.

Reductive Amination of Aldehydes and Ketones with Sodium Triacetoxyborohydride. Studies on Direct and Indirect Reductive Amination Procedures(1)

Sodium triacetoxyborohydride is presented as a general reducing agent for the reductive amination of aldehydes and ketones. Procedures for using this mild and selective reagent have been developed for a wide variety of substrates. The scope of the reaction includes aliphatic acyclic and cyclic ketones, aliphatic and aromatic aldehydes, and primary and secondary amines including a variety of weakly basic and nonbasic amines. Limitations include reactions with aromatic and unsaturated ketones and some sterically hindered ketones and amines. 1,2-Dichloroethane (DCE) is the preferred reaction solvent, but reactions can also be carried out in tetrahydrofuran (THF) and occasionally in acetonitrile. Acetic acid may be used as catalyst with ketone reactions, but it is generally not needed with aldehydes. The procedure is carried out effectively in the presence of acid sensitive functional groups such as acetals and ketals; it can also be carried out in the presence of reducible functional groups such as C-C multiple bonds and cyano and nitro groups. Reactions are generally faster in DCE than in THF, and in both solvents, reactions are faster in the presence of AcOH. In comparison with other reductive amination procedures such as NaBH(3)CN/MeOH, borane-pyridine, and catalytic hydrogenation, NaBH(OAc)(3) gave consistently higher yields and fewer side products. In the reductive amination of some aldehydes with primary amines where dialkylation is a problem we adopted a stepwise procedure involving imine formation in MeOH followed by reduction with NaBH(4).

Asymmetric syntheses, opioid receptor affinities, and antinociceptive effects of 8-amino-5,9-methanobenzocyclooctenes, a new class of structural analogues of the morphine alkaloids

Several 8-amino-5,9-methanobenzocyclooctenes have been prepared by asymmetric organic synthesis techniques. Opioid receptor affinity studies have revealed the virtual absence of enantioselectivity for receptor binding, particularly at the mu-receptor, for the (+)-3a-f and the (-)-3a-f series. It is noteworthy that inversion of configuration at the nitrogen-bearing carbon atom [5S,8S,9S)-8-amino-3-hydroxy-5, 9-methano-9-(methoxymethyl)-5-methylbenzocyclooctene, (+)-3a vs (5S,8S,9R)-8-amino-3-hydroxy-5, 9-methano-9-(methoxymethyl)-5-methylbenzocyclooctene, (dl)-22] resulted in a > 10-fold increase in kappa-receptor affinity. Antinociceptive studies demonstrated that (dl)-22 was a full kappa-agonist while (+)-3a and (-)-3a did not possess kappa-activity. Although both (dl)-22 and (+)-3a/(-)-3a had high affinity for the mu-receptor, these compounds did not act as high-affinity agonists or antagonists at this receptor.

Total Synthesis of (+)-Papuamine: An Antifungal Pentacyclic Alkaloid from a Marine Sponge, Haliclona sp

The total synthesis of (+)-papuamine, the antipode of the C(2)-symmetric, optically active, pentacyclic diamine natural product, starting from a chiral diol is described. The diol is available via an asymmetric Diels-Alder reaction between 1,3-butadiene and di-(-)-menthyl fumarate. The key transformation in the synthesis is an intramolecular Pd(0)-catalyzed (Stille) coupling reaction to form the central 13-membered diazadiene macrocyclic ring.