Synthesis of Polyhydroxylated Quinolizidine and Indolizidine Scaffolds from Sugar-Derived Lactams via a One-Pot Reduction/Mannich/Michael Sequence

Synthetic strategy for polyhydroxylated indolizidine iminosugar from sugar-derived HWE precursor

The diversity of polyhydroxylated indolizidine (PI) iminosugars is ever-expanding due to the wide range of methods developed and substrate choice during synthesis. This study used an HWE precursor derived from d-glucose to extend the chain length at the C1 position. A double reductive amination and dihydroxylation of the resulting olefin, followed by intramolecular cyclization, enabled the successful synthesis of a new PI. In addition, the precursor intermediate for Mitsunobu reaction was utilized in synthesis of a new iminononulol.

A Simple Entry to the 5,8-Disubstituted Indolizidine Skeleton via Hetero Diels-Alder Reaction

The 5,8-disubstituted indolizidines are the largest family of indolizidines isolated from the skin of amphibians. These compounds exhibit interesting biological activities such as noncompetitive blockers of nicotinic receptors. In this paper, we present a short, simple, and general synthesis of these alkaloids based on the hetero Diels-Alder reaction between suitable monoactivated dienes and Δ1-pyrroline as the dienophile. The selectivity of the process is explained based on computational studies. Concise synthesis of the indolizidine alkaloid 181B from a hetero Diels-Alder reaction was accomplished in four steps.

Stereoselective Synthesis of 1-C-Diethylphosphonomethyl and -difluoromethyl Iminosugars from Sugar Lactams

A strategy allowing the straightforward synthesis of 1-C-phosphonomethyl and 1-C-phosphonodifluoromethyl iminosugars is reported. Conversion of sugar lactams to the corresponding imines with Schwartz's reagent followed by their reaction with LiCH₂P(O)(OEt)₂ and LiCF₂P(O)(OEt)₂ stereoselectively afforded the 1,2-cis and 1,2-trans glycosyl phosphonates, respectively, in modest to good yields. Application of this methodology to C-2 orthogonally protected sugar lactams paved the way to 2-acetamido- and 2-deoxy-1-C-phosphonomethyl iminosugars.

Total Synthesis of (±)-Furanether A

The first total synthesis of (±)-furanether A, which exhibits good antifeedant activity, has been concisely achieved in 13 linear steps. Notably, the key rigid tetracyclic skeleton containing a 1-methyl-8-oxabicyclo[3.2.1]octane moiety with two vicinal quaternary carbon centers was rapidly constructed in one step through a unique tandem C-H oxidation/oxa-[3,3] Cope rearrangement/aldol cyclization sequence.

A Convenient Approach towards the Synthesis of ADMDP Type Iminosugars and Nojirimycin Derivatives from Sugar-Derived Lactams

An efficient method for the synthesis of nojirimycin- and pyrrolidine-based iminosugar derivatives has been developed. The strategy is based on the partial reduction in sugar-derived lactams by Schwartz’s reagent and tandem stereoselective nucleophilic addition of cyanide or a silyl enol ether dictated by Woerpel’s or diffusion control models, which affords amino-modified iminosugars, such as ADMDP or higher nojirimycin derivatives.

Concise synthesis of bicyclic iminosugars via reductive functionalization of sugar-derived lactams and subsequent RCM reaction

An efficient method for the synthesis of bicyclic iminosugars has been developed. The strategy is based on the partial reduction of sugar-derived lactams by Schwartz's reagent and tandem stereoselective nucleophile addition dictated by Woerpel's model which affords polyhydroxylated cyclic amines as key intermediates. Introduction of a vinyl or allyl group to the iminosugar produces diene derivatives that can be subjected to the ring-closing metathesis reaction (RCM) to furnish polyhydroxylated pyrrolizidine, indolizidine and quinozilidine derivatives in good to excellent yields. This sequence of reactions has been applied to the formal synthesis of hyacinthacine A₂, a polyhydroxylated pyrrolizidine alkaloid.

Direct synthesis of anomeric tetrazolyl iminosugars from sugar-derived lactams

Herein we present the direct asymmetric synthesis of tetrazole-functionalized 1-deoxynojirimycin derivatives from simple sugars via a Schwartz’s reagent-mediated reductive amide functionalization followed by a variant of the Ugi–azide multicomponent reaction. The anomeric configurations of two products were unambiguously confirmed by X-ray analysis. This work also describes examples of interesting further transformations of the title products. Finally, some surprising observations regarding the mechanism of their formation were made.

Iridium-Catalyzed Reductive Nucleophilic Addition to Secondary Amides

An iridium-catalyzed reductive nucleophilic addition to secondary amides is reported. After the iridium-catalyzed reduction, the resulting imines can undergo the Strecker reaction, the Mannich reaction, allylation, and [3 + 2]-cycloaddition. The method shows high chemoselectivity in the presence of other functional groups such as methyl ester.

Asymmetric synthesis of (-)-sedacryptine through a diastereoselective Mannich reaction of N,O-acetals with ketones

An efficient diastereoselective approach to access the 3-hydroxy-2,6-disubstituted piperidine scaffold 1 has been developed through the Mannich process involving N,O-acetal (2S,3R)-6 and ketones in excellent yield with high diastereoselectivity (dr > 99 : 1). In addition, the utility of this convenient one-pot process is demonstrated by the asymmetric synthesis of (-)-sedacryptine 3.

Iminosugar C-Nitromethyl Glycoside: Stereoselective Synthesis of Isoxazoline and Isoxazole-Fused Bicyclic Iminosugars

A simple and efficient method for the stereoselective synthesis of isoxazoline/isoxazole-fused iminosugar derivatives has been developed using intramolecular nitrile oxide cycloaddition (INOC) as a key step. Iminosugar C-nitromethyl glycosides, derived from simple carbohydrates, served as excellent nitrile oxide precursors in 1,3-dipolar cycloaddition reactions. N-Alkenyl iminosugar C-nitromethyl glycosides afforded novel isoxazoline-fused indolizidine-, pyrrolizidine-, and quinolizidine-based iminosugars in excellent yields with a high degree of stereoselectivity, whereas N-alkynyl iminosugar C-nitromethyl glycosides furnished the corresponding isoxazole containing tricyclic iminosugars in very good yields.

Stereoselective strategies for the construction of polysubstituted piperidinic compounds and their applications in natural products’ synthesis

An abridged and far-reaching review communication on the construction of the polysubstituted piperidinic core using diverse methodologies for the benefit of organic chemists interested in the total synthesis of biologically active compounds.

Cyclic enaminones. Part I: stereocontrolled synthesis using diastereoselective and catalytic asymmetric methods

Cyclic enaminones are versatile intermediates to construct a variety of azacyclic frameworks and have been widely used in alkaloid synthesis. Here, we summarize three approaches for stereoselective syntheses of cyclic enaminones and their functionalized derivatives. These include chiral substrates (chirons) as starting materials, syntheses employing non-catalytic (stoichiometric) reagents, and catalytic asymmetric methods.