Synthesis of 2,4,6-Trisubstituted Pyridines by Oxidative Eosin Y Photoredox Catalysis

Eosin Y, an organic dye, was activated as a photoredox catalyst in the presence of molecular oxygen using visible light and, when it was used in the reaction of aryl ketones and benzyl amines, afforded good yields (52–87%) of 2,4,6-triarylpyridines (21 examples) at ambient temperature. The aryl groups at the 2- and 6-positions are derived from ketones, while benzyl amine plays the dual role of providing an aryl functionality at the 4-position of pyridine as well as being a nitrogen donor

Synthesis of Pentahydroxy Indolizidine Alkaloids Using Ring Closing Metathesis: Attempts To Find the Correct Structure of Uniflorine A

Ring closing metathesis of d-glucose derived diene-substrate containing nitrogen functionality followed by asymmetric dihydroxylation afforded sugar substituted dihydroxylated pyrrolidines 8a−c which on 1,2-acetonide deprotection and reductive amination afforded putative uniflorine A 2a and its analogues 2b−c, respectively

Synthesis of Griseolic Acid Analogues: Regioselective α-Facial [1,2]-Migration in the Rhodium Acetate Catalyzed Reaction of d-Glucose Derived α-Diazo-β-keto Ester

This paper describes an efficient route for the synthesis of known and novel griseolic acid analogues 1d and 1e, respectively. The key intermediate dioxabicyclo derivative 6, with the required stereochemical orientation at C6, was obtained by rhodium acetate catalyzed reaction of d-glucose derived α-diazo-β-keto ester 5 in a novel high-yielding methodology

Chiron Approach to the Synthesis of (2<i>S</i>,3<i>R</i>)-3-Hydroxypipecolic Acid and (2<i>R</i>,3<i>R</i>)-3-Hydroxy-2-hydroxymethylpiperidine from d-Glucose

The first chiron approach from d-glucose for the total synthesis of (2S,3R)-3-hydroxypipecolic acid (−)-1a and (2R,3R)-3-hydroxy-2-hydroxymethylpiperidine (−)-2a is reported. The synthetic pathway involves conversion of d-glucose into 3-azidopentodialdose (5) followed by the Wittig olefination and reduction to give the piperidine ring skeleton (8) with a sugar appendage that on cleavage of an anomeric carbon followed by oxidation gives (−)-1a which on reduction affords (−)-2a

Electronic Effects in Migratory Groups. [1,4]- versus [1,2]-Rearrangement in Rhodium Carbenoid Generated Bicyclic Oxonium Ylides

The variety of α-diazo β-keto esters (3a−f, 8a−f) with varying substituents (ED/EW) on the phenyl ring of the O-benzyl group were prepared. The rhodium(II) acetate catalyzed decomposition of diazo compounds in benzene reflux conditions. The ratio of 1,4 versus 1,2 migration product was determined. It was found that an increase in electron density on the benzylic carbon of the migrating group prefers 1,4 migration products (4, 9) while a decrease in electron density leads to a preponderance of 1,2 migration products (5, 10). The results obtained were correlated to the mechanistic aspect of the product selectivity. The intermediacy of the intramolecular oxonium ylide formation was demonstrated by crossover experiments. The preference for the formation of 2,3 sigmatropic rearrangement product over 1,2 and 1,4 was demonstrated by performing the reaction with α-diazo β-keto esters (13a, 13b) with O-allyl and O-propargyl at C3. The effect of solvent, temperature, and mole percentage of rhodium(II) acetate was also studied

A Synthesis of New Coumarin <i>C-</i>Glycosyl Derivatives^†

A Synthesis of New Coumarin C-Glycosyl Derivatives†</sup

An Efficient Synthesis of d-<i>e</i><i>rythro</i>- and d-<i>t</i><i>hreo</i>-Sphingosine from d-Glucose: Olefin Cross-Metathesis Approach

The d-erythro- and d-threo-sphingosine were synthesized via E-selective olefin cross-metathesis using a d-glucose-derived building block and long-chain terminal alkene

Electronic Effects in Migratory Groups. [1,4]- versus [1,2]-Rearrangement in Rhodium Carbenoid Generated Bicyclic Oxonium Ylides

The variety of α-diazo β-keto esters (3a−f, 8a−f) with varying substituents (ED/EW) on the phenyl ring of the O-benzyl group were prepared. The rhodium(II) acetate catalyzed decomposition of diazo compounds in benzene reflux conditions. The ratio of 1,4 versus 1,2 migration product was determined. It was found that an increase in electron density on the benzylic carbon of the migrating group prefers 1,4 migration products (4, 9) while a decrease in electron density leads to a preponderance of 1,2 migration products (5, 10). The results obtained were correlated to the mechanistic aspect of the product selectivity. The intermediacy of the intramolecular oxonium ylide formation was demonstrated by crossover experiments. The preference for the formation of 2,3 sigmatropic rearrangement product over 1,2 and 1,4 was demonstrated by performing the reaction with α-diazo β-keto esters (13a, 13b) with O-allyl and O-propargyl at C3. The effect of solvent, temperature, and mole percentage of rhodium(II) acetate was also studied

Intermolecular Michael Addition of Substituted Amines to a Sugar-Derived α,β-Unsaturated Ester: Synthesis of 1-Deoxy-d-<i>g</i><i>luco</i>- and -l-<i>i</i><i>do</i>-homonojirimycin, 1-Deoxy-castanospermine and 1-Deoxy-8a-<i>epi</i>-castanospermine

The synthesis of polyhydroxylated piperidine alkaloids, namely, 1-deoxy-d-gluco-homonojirimycin 3a, 1-deoxy-l-ido-homonojirimycin 3b, and indolizidine alkaloids 1-deoxy-castanospermine 5a and 1-deoxy-8a-epi-castanospermine 5b, has been achieved. The key step involved is the intermolecular Michael addition of benzylamine to α,β-unsaturated ester 1, derived from d-glucose, which afforded diastereomeric mixture of β-amino esters 6a and 6b with d-gluco- and l-ido- configuration at C5, respectively. Attempts were made to increase and/or alter the diastereoselectivity at the newly generated stereocenter. The high stereoselectivity, in favor of l-ido-isomer 6b, was achieved under kinetically controlled conditions by using lithium N-benzyl amide as a Michael donor. The β-amino esters 6a and 6b represent common intermediates to target molecules. Thus, LAH reduction of 6a and 6b, individually, gave β-amino alcohol 7a and 7b. Sequential hydrogenolysis, selective protection of the amino group, followed by hydrolysis of the 1,2-acetonide functionality, and hydrogenation gave 3a and 3b, respectively. On the other hand, the β-amino ester 6a was converted to γ-amino ester 13a by Arndt−Eistert synthesis, which on hydrogenolysis and treatment with sodium acetate gave γ-lactam 14a. The LAH reduction afforded pyrrolidene. The N-protection−hydrolysis−hydrogenation cascade successfully executed, and 1-deoxy-castanospermine 5a was obtained in good yield. The same sequence of reactions was applied to β-amino ester 6b, which afforded 1-deoxy-8a-epi-castanospermine 5b

Asymmetric Dihydroxylation of d-Glucose Derived α,β-Unsaturated Ester: Synthesis of Azepane and Nojirimycin Analogues

The asymmetric dihydroxylation of a d-glucose derived α,β-unsaturated ester 3 afforded syn vicinal diols in good to high diastereoselectivity. The conversion of these vicinal diols to the corresponding cyclic sulfate, regio-, stereoselective nucleophilic ring opening by sodium azide, and LAH reduction afforded amino heptitols 7a,b that were converted to azepane 1c,d and nojirimycin analogues 2c,d