A concise approach to chiral chromenes based on levoglucosenone

Levoglucosenone, a chiral α,β-unsaturated ketone derived from cellulose, undergoes a stereoselective domino oxa-Michael-aldol reaction with 2-hydroxybenzaldehydes affording optically active pyrano[3,4-b]chromenes. The latter are further converted into 2H-chromenes via a Beckmann fragmentation reaction.     

Preparation of chiral cyclopropanes with a carbohydrate fragment from levoglucosenone

Levoglucosenone (a chiral α,β-unsaturated ketone derivative of cellulose) underwent stereoselective cyclopropanation with sulfonium ylides to form chiral trisubstituted cyclopropanes annulated with the carbohydrate moiety in high yields.     

Synthesis of a simple chiral auxiliary derived from levoglucosenone and its application in a Diels-Alder reaction

The synthesis of a chiral alcohol derived from levoglucosenone has been studied. The alcohol was employed as chiral template in an asymmetric Diels-Alder reaction of the corresponding acrylic ester derivative with cyclopentadiene, and was shown to be an efficient asymmetric inductor. The oxidation reaction detected during the hydrogenation of a secondary allylic alcohol intermediate with Pd/C was also investigated.     

A chiral auxiliary derived from levoglucosenone in asymmetric Diels-Alder transformations

The Diels-Alder reaction of the acrylate derived from levoglucosenone with cyclopentadiene was studied under several conditions, in the presence and absence of a Lewis acid. The results showed satisfactory diastereomeric excess and the ratio of cycloadducts was found to depend on the reaction conditions. A reversal in stereoselectivity was observed when EtAlCl₂ or Et₂AlCl were employed as Lewis acids.     

Highly diastereoselective Diels-Alder reaction using a chiral auxiliary derived from levoglucosenone

[reaction: see text] A new chiral auxiliary derived from levoglucosenone is reported. The compound is obtained by a cycloaddition reaction with 9-methoxy methylanthracene followed by a diastereoselective reduction of the C-2 keto function. The auxiliary has been used as a chiral template in an asymmetric Diels-Alder reaction of the corresponding acrylic ester derivative with cyclopentadiene. The results showed excellent diastereomeric excess even at room temperature when the reaction was promoted by Et(2)AlCl as the Lewis acid.     

Synthesis of levoglucosenone oxazoline derivative

Russian Journal of Organic Chemistry -     

A novel design of a levoglucosenone derived chiral auxiliary

A two-step general approach to a new chiral auxiliary starting from levoglucosenone is reported. The compound is obtained by a [4+2] cycloaddition reaction with anthracene followed by a diastereoselective reduction of the C-2 keto function in high overall yield. The auxiliary has been used as chiral template in an asymmetric Diels-Alder reaction of the corresponding acrylic ester derivative with cyclopentadiene and shown to be efficient for asymmetric induction.     

Synthesis of 1-benzoxepines from dichlorocarbene adducts of chromenes

Synthesis of 1-benzoxepines by dehydrochlorination of carbene adducts of chromenes has been carried out. Different alkyl-, alkylidene-, alkoxy-, aryl- and hetarylsubstituted 1-benzoxepines were obtained.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 188–194, February, 1987.     

Synthesis of 2-amino derivatives of levoglucosenone

2-Amino derivatives of levoglucosenone were prepared by reaction of the 2-methanesulfonyl (or p-toluenesulfonyl) derivatives with ammonia, methylamine, or octylamine under various conditions. The analogous reaction did not occur for saturated derivative 15. The 2-amino-3,4-dihydro derivative was prepared by catalytic hydrogenation of unsaturated amine 9.Translated from Khimiya Prirodnykh Soedinenii, No. 6, pp. 429–432, November–December, 2004.This revised version was published online in April 2005 with a corrected cover date.     

Exploring structural effects of levoglucosenone derived chiral auxiliaries in asymmetric Diels-Alder cycloadditions

New chiral auxiliaries derived from levoglucosenone were developed in a simple and efficient way and evaluated as chiral inductors in asymmetric Diels-Alder reactions between the corresponding acrylate derivatives and cyclopentadiene. The results showed an important influence of the absolute configuration of the C(2) center of the auxiliary on the level of stereoinduction obtained.     

Enantioselective organocatalytic synthesis of the chiral chromenes by domino oxa-Michael-aldol reaction

The proline based chiral organocatalyst has been found to be an efficient catalyst for enantioselective domino oxa-Michael-aldol reaction. This catalytic system provided the synthesis of substituted 2-aryl-2H-chromenes-3-carbaldehyde in good to high yields (73%–97%) with excellent enantioselectivity (up to 97%) and reasonable reaction times. The atom economy, high yield and mild reaction conditions are some of the important features of this protocol.     

Synthesis of carboxy-2,2-dimethylchromans and chromenes

The condensation of hydroxybenzoic acids, viz., 2,5-dihydroxy-, 3,5-dihydroxy-, 3,4,5-trihydroxy- and 2,4,6-trihydroxybenzoic acid with 2-methyl-but-1,3-diene (isoprene) in presence of orthophosphoric acid giving corresponding carboxy-2,2-dimethylchromans is described. 2,2-Dimethylchromans have been dehydrogenated withDDQ to give corresponding carboxy-2,2-dimethylchromenes.     

Synthesis of 6-carboxy-2,2-dimethylchromans and chromenes

The condensation of hydroxybenzoic acids and their methyl esters with isoprene in the presence of orthophosphoric acid gives corresponding 2,2-dimethylchromans, which can be dehydrogenated with DDQ or NBS to give the corresponding 6-carboxy-2,2-dimethylchromenes. The synthesis of β-tubaic acid, a natural compound, has also been achieved.     

One-pot approach to chiral chromenes via enantioselective organocatalytic domino oxa-Michael-aldol reaction

A highly enantioselective (S)-diphenylpyrrolinol triethylsilyl ether promoted tandem oxa-Michael-aldol reaction of alpha,beta-unsaturated aldehydes with salicylaldehydes has been developed; the method affords one-pot access to chiral and synthetically useful chromenes in high yields and high enantioselectivities from readily available compounds.     

Studies of substituent effect on asymmetric epoxidation of chromenes by chiral dioxirane

A series of 6- and 8-substituted chromenes has been investigated for asymmetric epoxidation using chiral ketone catalysts. Up to 93% ee was achieved. Higher ee's are obtained when substrates are substituted at the 6-position. The enhanced enantioselectivity is likely due to the beneficial interaction between the 6-substituent of the substrate and the N-aryl or alkyl group of the ketone catalyst.     

Synthesis and fungicidal activity of methylsulfanylmethyl ether derivatives of levoglucosenone

Chemistry of Heterocyclic Compounds - A series of derivatives were synthesized on the basis of levoglucosenone that contained hydroxy groups at the С-4 atom or С-2 and С-4 atoms...     

Eleuthesides and their analogs: I. Synthesis of the base compound from levoglucosenone adduct with piperylene

The Diels-Alder adduct of levoglucosenone and piperylene was converted into the corresponding oxime, and second-order Beckmann rearrangement of the latter, followed by treatment with a base, gave (1S,2R,6R)-6-(2-hydroxyethyl)-2-methylcyclohex-3-ene-1-carbaldehyde which was used in the synthesis of eleutheside analog. Conditions were found for opening of oxirane ring with formation of primary alcohol and simultaneous reduction of cyano group to aldehyde by the action of Red-Al-H₂O.     

Synthesis of alexine-like compounds from chiral five-membered endocyclic enecarbamates

Stereoselective syntheses of enantiomerically enriched trihydroxy pyrrolizidine and indolizidines were accomplished from a common chiral endocyclic enecarbamate. The synthetic strategy features an efficient [2+2] cycloaddition of ketenes to the endocyclic enecarbamate and a highly regioselective Baeyer-Villiger oxidation of the intermediate azabicyclic-cyclobutanones. These new heterocycles are compounds structurally related to the alexines.