Di-t-butyl azodicarboxylate

Enolate Amination. Amination likewise can be effected using Di-t-butyl Azodicarboxylate (DBAD). Despite the excellent yields and diastereoselectivity obtained using this methodology (eq 24), the harsh conditions required for further transformation of the resultant hy drazide adducts (Triftuoroacetic Acid and hydrogenation at 500 psi over Raney Nickel catalyst) limit its synthetic utility. 

Enolate anions derived from syn and anti 2-substituted 2-acyl-13-dithiane 1-oxides react readily with the nitrogen electrophile di-t-butyl azodicarboxylate (DBAD) to give a-aminoketones with good diastereoselectivity and in moderate yields (Scheme 4.64) [121]. A low-temperature acetic acid quench is necessary and is believed to prevent loss of stereochemical integrity at the new asymmetric centre which can otherwise occur. 

In related procedures that are based on lithium enolates of Evans Af-acyl oxazohdinones, azodicarboxylates 477 are used as electrophiles [228]. Excellent diastereoselectivity and high chemical yields in the formation of hydrazines 478 are reached with Af-acyl oxazohdinones 468 (R = CHjPh) and di-t-butyl azodicarboxylate (Scheme 4.101) [228a]. For the cleavage of the chiral auxihary from the substrate, saponification (LiOH in THF/water) and transesterification methods (A4eA4gBr in methanol or LiOCH2Ph in THF) were developed and occurred without significant racemization in the esters or acids 479, except for... 

Experimental procedure for the [4-1-2] cycloaddition of azo dienophile 209 A solution of the diene 210a (3.40 g, 7.4 mmol) and di-t-butyl azodicarboxylate 209 (5.10g, 22.1 mmol) in dry dichloromethane (80 mL) was heated up under reflux for 5 days. Evaporation of the solvent and subjection of the residue to column chromatography gave two fractions. The first fraction (eluted with hexanes-Et20 1 1) was the unchanged azodicarboxylate. The second fraction (eluted with Et20) was the title compound 212a (3.94 g, 77%) as a foam. 

Di-t-butylN-alkylhydrazine-N,N -dicarboxylates. These compounds are obtained by addition of organozinc reagents (RX -1- Zn ) to di-f-butyl azodicarboxylate. 

Synthetic Methods.—The preparation of phosphate esters by 5n2 attack of phosphate ester anions on carbon is receiving more attention following the realization that the poor nucleophilicity commonly associated with such anions is due to solvation and ion-pairing effects. Thus tetra-methylammonium di-t-butyl phosphate reacts with primary and secondary alkyl iodides in aprotic solvents to give the corresponding triesters (1) from which the t-butyl groups are readily removed by trifluoracetic acid. The proposal of a similar S 2 mechanism in the reaction of triphenylphosphine and ethyl azodicarboxylate with a phosphate diester in the presence of an... 

Melchiorre and co-workers [55] demonstrated the efficiency of the TEA salt of 9-amino-(9-deoxy)-epi-hydroquinine 21 in promoting an iminium/enamine cascade sequence including a sulfa-Michael followed by an amination reaction (Figure 14.6). The reaction of a,(3-disubstituted enals with t-butyl or benzyl mercaptan and di-t-butoxycarbonyl azodicarboxylate enabled the formation, in excellent levels of enantioselectivity, of valuable precursors of a-amino acids containing two contiguous stereocenters, one of which is quaternary (Scheme 14.19). The diastereomeric ratio of products was also satisfactory. 

One of the first attempts to determine Mc,chcm was made by Flory et al. (1949). They believed that bis-azodicarboxylates were quantitative in their cross-linking reaction of diene rubbers, an assumption subsequently questioned by Moore and Watson (1956). As an alternative these workers used di-t-butyl peroxide to vulcanize natural rubber and were able to quantitatively account for all the reaction products. The work of Moore and Watson is today regarded as a model of painstaking experimental technique and will now be considered in some detail. 

This reaction has been extensively modified, including the fixation of phosphine and dialkyl azodicarboxylate onto a polymer or fluorous reagent and the introduction of a basic moiety to a phenylphosphine. In addition, bis(2-(l-adamantyl)ethyl) azodicarboxylate (BadEAD), bis(l-adamantylmethyl) azodicarboxylate (BadMAD), bis(5-norbornen-2-ylmethyl) azodicarboxylate (DNAD), di-t rt-butyl azodicarboxylate (DBAD), fluorous azodicarboxylate (FDEAD), A,A,A, A -tetramethylazodicarboxamide (TMAD), and l,T-(azodicarbonyl)dipiperidine (ADDP), have also been developed for the Mitsunobu reaction. 

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