Stereoselective synthesis of 2,2-bis(C-branched-chain) glucopyranosid-3-ulose via autoxidation reaction

Many different approaches for synthesis of branched chain sugars have beenestablished,1 because they are very useful intermediates for synthesis of other non-sugar chiralmolecules, and usually occur in nature. Branched chain glycosidulose can be used for construction offive- and six-membered carbocyclic rings to which two chiral carbons of sugar are incorporated byintramolecular aldol condensation and Robinson annulation,2 Therefore they are useful in thesynthesis of natural products which consist of annulated carbohydrates or where a highlyfunctionalised enantiomerically pure cyclopentane or cyclohexane is required. Also, this type ofbranched chain sugar can be considered as the synthons of monoterpenoid natural products of theiridoid class which have the cyclopentan-(c)-pyran structure. In view of the importance of branchedchain glycosiduloses, it is desirable to have a general, convenient methodology to their synthesis.However, none of the literature methods was reported on their synthesis by a nuclephilic addition toa partially protected glycosidulose, due to the fact that these glycosiduloses are very difficult tosynthesize selectively and unstable;3 and what is more, one-step synthesis branched chainglycosidulose using this method is almost impossible.In this paper, we report on a general, convenient method for stereoselective syntheses of2,2-bis(C-branched-chain)glucopyranosid-3-uloses by the new reaction of 1 with various activemethylene compounds. The generality of this method was examined in detail. The optimumtemperature was 18-25℃. The solvent DMF was better than the others. In all cases he yields werehigher than 60%.All the 2,2-bis(C-branched-chain)glucopyranosid-3-uloses were characterized by X-raycrystallographic analyses. In addition, the important iintermediate in this reaction was isolated,which is the product of autoxidation of 1 at C-3 position. Thus the reaction mechanism for thesynthesis of 2,2-bis(C-branched-chain) glucopyranosid-3-uloses can be rationalized by autoxidationof 1 followed by 1,4-Michael addition of various carbanions as the main steps.     

Stereoselective synthesis of cembranolides via conjugate addition to cycloalkynones

Addition of lithium dimethylcuprate to the conjugated cycloalkynone 8 yielded, after equilibration, a single (E)-enone 10 which was converted via acidic hydrolysis, oxidation, and reduction to the cis lactone 14. α-Methylenation afforded the natural cembranolide 16.     

Stereoselective synthesis of functionalized trisubstituted olefins via palladium(0)-catalyzed cross-coupling reaction

[reaction: see text]. A highly flexible and stereoselective protocol for the synthesis of branched (E)- and (Z)-trisubstituted alkenes has been developed. The key steps are hydrozirconation-iodination of (1-alkynyl)trimethylsilane followed by Negishi-type cross-coupling. The resultant (Z)-vinyl silane is iododesilylated and subjected to a second cross-coupling reaction to give the trisubstituted olefin. Model studies aimed at the construction of the C14-C15 (Z)-trisubstituted olefin of discodermolide and the C8-C9 (Z)-trisubstituted olefin of callystatin A and analogues are also described.     

Stereoselective construction of cis-2,6-disubstituted tetrahydropyrans via an intramolecular bismuth-mediated oxa-conjugate addition reaction

The intramolecular oxa-conjugate addition of tethered triethylsilyloxy substituted α,β-unsaturated ketones mediated by bismuth(III) nitrate pentahydrate provides a mild and efficient method for the stereoselective construction of cis-2,6-disubstituted tetrahydropyrans.     

Stereoselective synthesis of β-carboethoxy-γ-lactams via imino Mukaiyama aldol-type reaction of 1,4-bis(trimethylsilyloxy)-1,4-diethoxy-1,3-butadiene

The reaction of the (bis)trimethylsilyloxy derivative of diethyl succinate with imines in the presence of ZnCl₂ provides a general stereoselective entry to β-carboethoxy-γ-lactams.     

Novel synthesis of 2,2-bis(2-methoxy-1-oxidodiazenyl)ethylnitramines via the relative ethyl trifluoroacetate

Russian Chemical Bulletin - A novel synthesis of 2,2-bis(2-methoxy-1-oxidodiazenyl)ethyl derivatives of methylnitramine and ethylenedinitramine consists in the treatment of...     

An unusual reaction of 1,1-dicyano-2,2-bis(trifluoromethyl)ethylene

Translated from Izvestiya Akademii Nauk SSSR, Seriya KMmicheskaya, No. 6, pp. 1451–1452, June, 1988.     

Stereoselective synthesis of the octahydronaphthalene unit of integramycin via an intramolecular Diels-Alder reaction

[reaction: see text] The racemic cis-decalin core fragment 30 of integramycin was synthesized by a sequence involving a highly diastereoselective intramolecular Diels-Alder reaction of triene 24. A remarkable switch in stereoselectivity occurred upon changing the dienophile unit of 24 from (Z)- to (E)-geometry.     

Stereoselective synthesis of 6-oxabicyclo[3.2.1]octene via (3,5)-oxonium-ene reaction

Oxabicyclo[3.2.1]octene can efficiently be synthesized by the reaction of (?)-terpinen-4-ol and aldehyde or epoxide catalyzed by indium triflate (In(OTf)₃) in good yields. The reaction is stereoselective and proceeds via (3,5)-oxonium-ene-type reaction.     

Stereoselective synthesis of (E)-α-aryltellurenylvinylsilanes via hydromagnesiation reaction of alkynylsilanes

(E)-α-Aryltellurenylvinylsilanes have been synthesized stereoselectively via the hydromagnesiation of alkynylsilanes, followed by the reaction with aryltellurenyl iodides. (E)-α-Aryltellurenylvinylsilanes can undergo the cross coupling reaction with Grignard reagents in the presence of Ni(PPh₃)₂Cl₂ catalyst to afford (Z)-1,2-disubstituted vinylsilanes in good yields.     

Stereoselective synthesis of 3,4-di-substituted mercaptolactones via photoredox-catalyzed radical addition of thiophenols

A visible light mediated radical addition of thiophenols on 4-phenylbut-3-enoic acids to give diastereoselective synthesis of 3,4-disubstituted γ-lactones is reported. The reaction precludes the conventional prerequisite of conjugate addition. Furthermore, the lactones were successfully utilized in the synthesis of γ-ketoamides.     

Stereoselective synthesis of highly functionalized nitrocyclopropanes via organocatalyic conjugate addition to nitroalkenes

A convenient and novel one-pot organocatalytic methodology for the stereoselective synthesis of highly functionalized nitrocyclopropanes is reported. The addition of dimethyl chloromalonate to a variety of nitroolefins catalyzed by tertiary amines leads to a Michael adduct which cyclizes to form the cyclopropane in the presence of DBU under carefully controlled reaction conditions with outstanding diastereoselectivity.     

Stereoselective synthesis of cycloheptanone derivatives via an intermolecular [5 + 2] cycloaddition reaction

[reaction: see text] A [5 + 2] cycloaddition reaction of a new five-carbon unit was developed on the basis of a dicobalt hexacarbonyl propargyl cation species. Under the influence of EtAlCl(2), [5-benzoyloxy-2-(triisopropylsiloxy)-1-penten-3-yne)]dicobalt hexacarbonyl reacted with enol triisopropylsilyl ethers to yield seven-membered dicobalt acetylene complexes in good yield. The reactions with cyclic enol silyl ethers as well as acyclic enol silyl ethers exhibited remarkably high diastereoselectivity. The cycloadducts can be easily converted into various kinds of cycloheptanone derivatives.     

Stereoselective synthesis of tetra-substituted olefins via addition of zinc enolates to unactivated alkynes

[reaction: see text] In the presence of a stoichiometric or catalytic amount of diethylzinc, a beta-aminocrotonamide undergoes sequential addition/isomerization reactions with 1-alkyne to produce, upon hydrolysis, an alpha-alkylidene beta-dicarbonyl compound in a highly stereoselective manner. The method complements the conventional Knoevenagel synthesis of this class of compounds as to the choice of the starting material and the scope and stereochemistry of the product.     

Stereoselective synthesis of 3-alkylideneoxindoles via palladium-catalyzed domino reactions

We have developed efficient catalytic methods for the stereoselective and diversity synthesis of various (E)-, (Z)-, and disubstituted 3-alkylideneoxindoles and 3-alkylidenebenzofuran-2-ones via palladium-catalyzed Heck/Suzuki-Miyaura, Heck/Heck, and Heck/carbonylation/Suzuki-Miyaura domino reactions.     

Stereoselective synthesis of 3-butylphtalide via CBS catalytic reduction

Optically active 3-butylphtalide of high enantiomeric excesses (up to 93% e.e.) was synthesized from the reduction of o-pentanoylbenzoic ester with borane using B-methyloxyoxazaborolidine (1b) as the chiral catalyst.