Epoxide with azide

Figure 7.2 Biologically interesting molecules prepared by (salen)chromium-catalyzed ARO of epoxides with azide.

Subsequent to the development of the (salen)Cr-catalyzed desymmetrization of meso-epoxides with azide (Scheme 7.3), Jacobsen discovered that the analogous (salen)Co(n) complex 6 promoted the enantioselective addition of benzoic acids to meso-epoxides to afford valuable monoprotected C2-symmetric diols (Scheme 7.15) [26], Under the reaction conditions, complex 6 served as a precatalyst for the (salen) Co(iii)-OBz complex, which was fonned in situ by aerobic oxidation. While the enantioselectivity was moderate for certain substrates, the high crystallinity of the products allowed access to enantiopure materials by simple recrystallization. 

The synthesis of a,a-disubstituted amino acids is a difficult task and continues to attract attention. An efficient route that utilizes the ring-opening of an epoxide with azide has been reported <06TL9268>. Treatment of the sulfoxide substituted epoxide 23 with NaN3 provides intermediate azido aldehyde 24. This aldehyde was not isolated but oxidized to the acid and then the azide reduced to provide the a,a-disubstituted amino acid 25. The regioselectivity of this reaction was impressive with only one product reported. 

Scheme 6.132 Ring-opening of epoxides with azide ions.

P-Aminoalcohols may be generated from (3-azidoalcohols, which are commonly made from the opening of epoxides with azide ion as shown in Scheme 13 (91TL2533). After conversion of the alcohol... 

The enantioselective synthesis (51) of the side chain 30 of taxol had been achieved by way of stereospecific Sharpless epoxidation of cij-cinnamyl alcohol (29a), giving 29b (see Scheme 6). Following oxidation of the alcohol group, protection of the resulting carboxylic acid, regioselective opening of the epoxide with azide, benzoylation, and reduction, a suitably substituted moiety (28) was available which, after protection and deprotection of the acid function to form 30, was coupled to baccatin III. 

An indirect method for generating an amino alcohol (124) is to open an epoxide with azide to give the azido-alcohol 123, and subsequent reduction (19-50) gives the amine group.Sodium azide and Oxone react with epoxides to give an azi-do-alcohol. Under Mitsunobu conditions (10-17), epoxides are converted to 1,2-diazides with The reaction of trimethylsilyl azide and an epoxide was... 

Opening of epoxides with azide ions represents a very interesting route to azidocarbinols. The large number of examples quoted in the literature proves the broad scope of this technique." " On treatment of nonsymmetrically substituted oxiranes, the products expected from an 5n2 process are usually obtained. In boiling aqueous dioxane, cyclohexene oxide gives rise to 61% of rrans-2-azidocyclohexa-nol. The reported formation of (35 Scheme 46) with styrene oxide is unexpected, particularly if the formation of (36) from the analogous diphenyl precursor is considered. ... 

Cleavage of 5a,6a- and 6a,7a- epoxides with azide ion and subsequent reduction with hydrazine has led to the preparation of 6 -amino-steroids, although similar treatment of 16a,17a-epoxypregnenolone acetate was accompanied by D-homoannulation to give, after reduction, the 16j3-amino-Ha-ketone. Azide displacement (lithium azide in DMF) of 3a,20j8-diacetoxy-... 

Precursor azido sulfonates in the pyranose series are usually prepared by the cleavage of suitable epoxides with azide, followed by mesylation or tosylation. This approach was used for the preparation of methyl 4,6-0-benzylidene-2,... 

Besides biomimetic complexes, Jacobsen described particularly efficient bis (chromium-salen) catalyst 9 for the asymmetric ring-opening reaction of epoxides with azide (Scheme 9) [42]. The efficiency of this class of catalysts is attributed to a cooperative mechanism, both substrates being activated toward each other by their respective chromium atom. Of note, a less pronounced cooperative effect was initially demonstrated in an intermolecular manner using monomeric Cr(N3)-salen catalyst [43]. Jacobsen also showed that an analogous cooperative mechanism takes place using polymer-supported chiral Co(salen) complexes for the hydrolytic kinetic resolution of terminal epoxides [44, 45]. 

Azido-sugars are frequently prepared by reaction of epoxides with azide ion. 3-Azido-3-deoxy-L-threose 68 was synthesized from cu-but-2-ene-l,4-diol 66 via the Sharpless asymmetic epoxidation product 67, and was converted into 6-azido-6-deoxy-L-galocro-heptulose 69 by an enzyme-catalyzed aldol condensation (Scheme 13). 3-Azido-3-deoxy-L-etythrose, and thence 6-azido-6-deoxy-L-g/uco-heptulose were obtained in a similar way via 4-rerf-butyldiphenylsilyoxy-rraiu-but-2-enal. These and two other azido-heptulose isomers made from the enantiomeric 3-azido-3-deoxy-tetroses, were converted to a- and P-l-homonojirimycin and homomannonojirimycin on hydrogenation. Ethyl 3-azido-2,3-dideoxy-D-eryr/iro-pentopyranoside and its 3-C-methyl analogue 71, R=H or Me, were synthesized from crotonaldehyde or 3-methyl-2-... 

A range of indolo(triazolo)-l,4-diazepine derivatives 104 were obtained by a microwave-heated three-component reaction involving tandem N-alkylation of indole 101 with epichlorohydrin 102, ring-opening of the epoxide with azide 103, and intramolecular azide-alkyne 1,3-dipolar cycloaddition reactions (13BJO401). Fused triazolodiazepinones were obtained via azide-alkyne 1,3-dipolar cycloaddition followed by lactamization (13JHC430). 

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