Consolación Gasch

Simple and efficient conversion of N,N-dimethylhydrazones and aldehydes to nitriles.

Aldehyde N,N-dimethylhydrazones undergo facile oxidative cleavage to nitriles on reaction with magnesium monoperoxyphtalate hexahydrate (MMPP)

An easy route to seven-membered iminocyclitols from aldohexopyranosyl enamines

Abstract A new stereocontrolled and high yielding synthesis of biologically active polyhydroxyperhydroazepines is reported starting from easily available glycosylenamines (D- gluco , D- manno , and D- galacto configurations), which are transformed into 1,6-azaanhydropyranose derivatives. O - and N -Deprotection of the latter, followed by reduction with sodium cyanoborohydride, gives the target chiral iminocyclitols. The method is based on the capacity of the dialkoxycarbonylvinyl group to stabilize an amide ion, and the only limitation is the necessity for the starting glycosylenamine to have β-D-configuration. The inhibitory activity of several intermediate iminocyclitols and aldopyranosylenamines on different α- and β-glycosidases is also reported.

Isothiocyanato derivatives of sugars in the stereoselective synthesis of spironucleosides and spiro-C-glycosides

Abstract A stereocontrolled synthesis of pyranoid and furanoid spironucleosides and spiro- C -glycosides ( d - ribo and d - arabino configurations) of oxazolidines, oxazolines and perhydrooxazines via isothiocyanato sugar derivatives is reported. The intermediate isothiocyanates are prepared from sugar spiroketals by stereoselective opening of the acetal ring with trimethylsilyl N - and C -nucleophiles, and later formation of the isothiocyanato group.

Highly efficient nitroaldol reaction promoted by trialkylsilyl chlorides

β-Nitroalcohols can be readily obtained in high yields by the one-pot reaction of aldehydes with nitrecompounds in the presence of Et3N, Bu4NF·3H2O and tBuMe2SiCl. Model experiments indicated that trialkylsilyl nitronic esters are not reaction intermediates.

Formaldehyde dimethylhydrazone: A new neutral reagent for nucleophilic hydroformylation and hydrocyanation

Abstract The readily available title compound smoothly adds to nitroolefins without any need of base or catalysis, giving β-nitrodimethylhydrazones 3 in high yields. Michael adducts 3 have been successfully transformed into β-nitroaldehydes by ozonolysis and in β-nitronitriles in excellent yields by treatment with MMPP. Therefore, formaldehyde dimethylhydrazone behaves as a new neutral formyl anion and cyanide equivalent, introducing a functionalized carbon unit β to the nitro group of a nitroolefin. Good yields and high stereoselectivities were obtained in the addition of 1 to a nitroolefin group within sugar derivatives, and no epimerization was observed in the cleavage of the dimethylhydrazone group.

Isothiocyanatoulosonates, a new type of glycosyl isothiocyanate useful for the stereocontrolled synthesis of thiohydantoin spironucleosides

Abstract Thiohydantoin spironucleosides and N -alkyl, aryl and glycosyl derivatives are prepared in a stereocontrolled manner, by reaction of ammonia, and of alkyl-, aryl- and glycosyl-amines with a new class of isothiocyanato sugar: the methyl 2-deoxy-2-isothiocyanatohex-2-ulofura(pyra)nosonates. The reaction produces an intermediate thioureido derivative, which spontaneously cyclates to give the spironucleoside in high yield. Alternatively, the same spironucleosides are prepared from methyl 2-amino-2-deoxy-hex-2-ulofura(pyra)nosonates and alkyl-, aryl- and glycosyl isothiocyanates. Some of the prepared compounds have the structure of N -nucleoside of spirothiohydantoins.

Chiral thioxohydroimidazoles with two sugar moieties. N-, C-, and spiro-nucleosides

Abstract 2-Amino (alkyl and arylamino)-2-deoxy- d -fructose and different sugar isothiocyanates are used in the diastereoselective synthesis of chiral imidazolidine-2-thione N -nucleosides 12 – 23 . Water β-elimination of these compounds produces imidazoline-2-thione N -nucleosides 27 – 31 , whereas cyclodehydration of the same products gives, with high stereoselectivity, chiral spironucleosides with an N -glycosyl radical 34 – 37 . Conformational aspects of some of the prepared compounds are discussed.

Asymmetric synthesis of functionalized nitrocompounds through Michael addition of formaldehyde SAMP hydrazone to nitroolefins

Abstract Chiral β-nitrohydrazones 7 can be easily prepared in good yields and diastereoselectivities by non catalyzed Michael addition of formaldehyde SAMP hydrazone 6 to simple nitroolefins.

Lengthening of the carbon chain of sugars by the Ch(NO2·CH(OEt)2 fragment a route to higher 2-amino-2-deoxyaldoses☆

Abstract Nitroaldol (Henry) reactions promoted by trialkylsilyl chlorides have been applied to the preparation of chain-extended nitro and amino sugars. The one-pot reaction of 1,2:3,4-di O -isopropylidine-α- d - galacto -hexodialdo-1, 5-pyranose ( 1 ) with 1,1-diethoxy-2-nitroethane in the presence of Et 3 N, Bu 4 NF ·3H 2 O, and t BuMe 2 SiCl yielded 7-deoxy-1,2:3,4-di- O -isopropylidene-7-nitro- l - threo-α- d -galacto -octodialdo-1, 5-pyranose diethyl acetal ( 3a ) and a diastereoisomer in the ratio 4:1. The structure of 3a was established by a single crystal X-ray diffraction study. Hydrogenation of 3a (Ni, H 2 ) afforded the corresponding 7-amino-7deoxyl-1,2:3,4-di- O -isoprpylidene- l - threo-α- d -galacto -octodialdo-1,5-pyranose diethyl acetal 4a ). Conversion of the latter compound into a trans -oxazoline derivative demonstrated that the l - threo configuration had been retained. Likewise, reaction of the aldehydo sugar 1 with 1-nitropropane was carried out in order to compare the efficiency of the new nitroaldol procedure here applied with that reported using trialkylsilyl nitronic esters as intermediates.

Synthesis of alkyl glyco-pyranosides and -furanosides of 2-amino-2-deoxy-d-glucose. Crystal structure of 2-deoxy-2-[(4,4-dimethyl-2,6-dioxocyclohexylidenemethyl)amino]-α-d-glucopyranose

Abstract The reaction of 2-amino-2-deoxy- d -glucose hydrochloride with 5,5-dimethyl-2-phenylaminomethylene-1,3-cyclohexanedione in MeOH in the presence of Et3N afforded 2-deoxy-2-[(4,4-dimethyl-2,6-dioxocyclohexylidenemethyl)amino]- d -glucose (6) in yields > 75%. Glycosidation of 6 with different alcohols (MeOH, CH2CHCH2OH, BnOH) under the Fischer conditions afforded mixtures of the corresponding alkyl 2-deoxy-2-[(4,4-dimethyl-2,6-dioxocyclohexylidenemethyl)-amino]-α,β- d -glucopyranoside and -α- d -glucofuranoside. Removal of the N-protecting group gave high yields of the free aminodeoxyglyco-pyranosides and -furanosides. In addition to other known glycosides, allyl and benzyl 2-amino-2-deoxy-α- d -glucopyranoside and ethyl and allyl 2-amino-2-deoxy-α-β-glucofuranoside were obtained. An X-ray crystallographic study of 6 indicated that, in the solid state, it has the α- d configuration and that the pyranoside ring adopts the 4C1 conformation.