Short and stereoselective synthesis of polysubstituted cyclohexanones

Two equivalents of dimethyl 1,3-acetonedicarboxylate reacted with α,β-unsaturated aldehydes to form novel polysubstituted cyclohexanones 2 in an efficient one-step procedure. The reactions proceeded at room temperature in the presence of catalytic amount of sodium methoxide, affording the products in high yields in a remarkably stereoselective manner. The products are of possible biological interest.     

A new method for the stereoselective synthesis of alpha-substituted serine amino acid analogues

[reaction: see text]. A new method was developed for the stereoselective synthesis of alpha-substituted serine amino acids. The strategy utilizes a common enantiomerically enriched intermediate obtained through an enzymatic desymmetrization. A variety of amino acids were synthesized in good ee's through nucleophilic acetylide addition reactions and palladium-catalyzed Sonogashira couplings.     

Sc3+-catalyzed aldol-type additions of N-benzoylcyclopropanecarboxamides via iodide-mediated ring-opening: stereoselective synthesis of gamma-lactams

A new catalytic aldol-type addition of cyclopropanecarboximides to aldehydes via iodide-mediated ring-opening is presented. The reaction was found to be catalyzed at 0 degrees C using either a Sc(OTf)3/NaI system or ScI3. Stereoselective formation of alpha,alpha-disubstituted enolates occurred in situ. gamma-Lactams bearing alpha-carbonyl quaternary stereocenters were obtained in 97-57% yield and dr = 90:10-80:20 after ring closure.     

Facile synthesis of alpha-substituted acrylate esters

Treatment of 5-monosubstituted Meldrum's acids with dimethylmethyleneimmonium iodide (Eschenmoser's iodide salt) in methanol gives alpha-substituted acrylate methyl esters in good yields. Easy access to 5-monosubstituted Meldrum's acids allowed us to synthesize a wide variety of alpha-substituted acrylate methyl esters. The reaction conditions are mild and tolerate many functional groups commonly used in organic synthesis; thus, this new method has potential as an alternative to conventional preparative methods for alpha-substituted acrylate esters.     

Short, stereoselective synthesis of C-glycosyl asparagines via an olefin cross-metathesis

The Grubbs second generation ruthenium catalyst was employed for the cross metathesis between α- and β-C-allyl glycosides and suitably protected l-vinyl glycines to furnish olefinic products in 57-94% yields. Hydrogenation afforded the C-glycosyl asparagines in high yield.     

Short and stereoselective synthesis of manzacidins A and C, and their enantiomers

A short and stereoselective synthesis of manzacidins A and C, and their enantiomers was achieved via stereoselective hydrogenation reactions of dehydroamino acid esters 5-8 using a chiral Rh catalyst.     

Short and efficient total synthesis of fraxinellone limonoids using the stereoselective Oshima-Utimoto reaction

[reaction: see text] The catalytic diastereoselective Oshima-Utimoto reaction was employed for the construction of fraxinellone and related members of this limonoid family of natural products. After formation of the five-membered lactone, a stereoselective aldol reaction and olefin metathesis established the bicyclic ring system in the natural products.     

Short, stereoselective synthesis of the naturally occurring pyrrolidine radicamine B and a formal synthesis of nectrisine

A short, stereoselective synthesis of the naturally occurring pyrrolidine radicamine B is reported. Garner's (R)-aldehyde, prepared from D-serine, was the chiral starting material. The pyrrolidine ring was stereoselectively created in a very efficient way through a five-step, one-pot transformation. In addition, an intermediate of this synthesis was transformed into an intermediate of a previously published synthesis of the potent alpha-glucosidase inhibitor nectrisine.     

Diastereoselective synthesis of gamma-lactams by a one-pot, four-component reaction

A new one-pot, four-component reaction (4CR) between amines, maleic anhydrides, aldehydes, and thiols has been discovered to form tetra- and pentasubstituted gamma-lactams with high diastereoselectivity. Each component is independently variable and employed in equivalent stoichiometry, producing only water as a byproduct.     

Short and stereoselective synthesis of C-glycosylated glycine derivatives from glycals by radical addition and reduction

Only three steps are required for the convenient synthesis of 2-C-branched glyco-amino acids from glycals with good yields and stereoselectivities.     

Efficient synthesis of gamma-lactams by a tandem reductive amination/lactamization sequence

A three-component method for the synthesis of highly substituted gamma-lactams from readily available maleimides, aldehydes, and amines is described. A new reductive amination/intramolecular lactamization sequence provides a straightforward route to the lactam products in a single manipulation. The general utility of this method is demonstrated by the parallel synthesis of a gamma-lactam library.     

A stereoselective synthesis of xylitol

Rel-(2S, 3R, 4R)- (6) and rel-(2R,3R,4R)- (7) 1,2,5-triacetoxy-3,4-epoxypentanes have been obtained in seven steps starting from cyclopentadiene. Both diastereoisomers afford xylitol pentaacetate (8) selectively upon epoxide cleavage with acetate ion. In the case of (6), rel-(1s,3R,4r,5S)-3,-bisacetoxymethyl-1-methyl-2,6,7-trioxabicyclo- [2.2.1]heptane (11) has been isolated and characterised as an intermediate in the reaction.     

Polymer-supported stereoselective synthesis of benzimidazolinopiperazinones

We describe the efficient synthesis of 4,7,8,10-tetrasubstituted-(((4S,10aS)-3-oxo-3,4,10,10a-tetrahydrobenzo[4,5]imidazo[1,2-a]pyrazin-2(1H)-yl)alkyl)amides on solid phase via tandem N-acyliminium ion cyclization-nucleophilic addition reactions. The synthesis proceeded with complete stereocontrol of a newly formed stereogenic center, provided crude material of high purity, and used commercially available building blocks under mild reaction conditions.     

Direct stereoselective synthesis of beta-thiomannosides

A highly diastereoselective synthesis of beta-thiomannopyranosides is described in which S-phenyl 2,3-di-O-benzyl-4, 6-O-benzylidene-1-deoxy-1-thia-alpha-D-mannopyranoside S-oxide is treated with triflic anhydride and 2, 6-di-tert-butyl-4-methylpyridine in CH(2)Cl(2) at -78 degrees C leading to the formation of an intermediate alpha-mannosyl triflate. Addition of primary, secondary, or tertiary thiols then leads to the beta-thiomannosides, by an S(N)2-like displacement, in good yield and with excellent stereoselectivity. Deprotection is achieved either by Birch reduction or by Zemplen deacetylation, of the acetyl protected aglycons, followed by hydrogenolysis over Pearlman's catalyst. The assignment of configuration of the beta-thiomannopyranosides is discussed in terms of the chemical shift of the mannose H5 resonance and the (1)J(CH) of the mannose anomeric carbon.     

Straightforward stereoselective synthesis of spiro-epoxyoxindoles

[reaction: see text] The in situ preparation of a sulfonium ylide reagent achieved the highly diastereoselective epoxidation of isatins, so that a new and straightforward access to biologically significant spiro-epoxyoxindoles is provided. The first investigations of an asymmetric version are reported with enantiopure sulfides.