Interpretation of conjugated oxiranes behavior toward nucleophiles

Influence of the methyl group in isoprene epoxides on reactivity compared to butadiene epoxides: Biological significance

Reactions of the epoxides of 1,3-butadiene and isoprene (2-methyl-1,3-butadiene) with oxygen, nitrogen and sulfur nucleophiles have been compared to enable a better molecular understanding of the relative human toxicities of these epoxides. Hydrolysis of rac.-ethenyloxirane in (¹⁸O)water gave 77% (2-¹⁸O)but-3-ene-1,2-diol and 23% (1-¹⁸O)but-3-ene-1,2-diol. The R:S ratio for but-3-ene-1,2-diol from hydrolysis of (S)-ethenyloxirane was 75:25. Hence, hydrolysis of ethenyloxirane occurs by competing S_N2 attack at C-2 and C-3 in 3:1 ratio, with no S_N1 component. Hydrolysis of rac.-2-ethenyl-2-methyloxirane gave 2-hydroxy-2-methylbut-3-en-1-ol (73%) and 27% of a 2:1 mixture of the E- and Z-isomers of 4-hydroxy-2-methylbut-2-en-1-ol. In (¹⁸O)water (2-¹⁸O)2-hydroxy-2-methylbut-3-en-1-ol was obtained. Formation of these products occurs via S_N1 ionisation to resonance-stabilised allylic cations which are captured by water. Reaction of rac.-ethenyloxirane with l-valine methyl ester gave diastereoisomeric adducts from S_N2 attack of the valine amino at both C-2 (substituted position) and C-3 of the oxirane. The corresponding reaction of rac.-2-methyl-2-ethenyloxirane gave diastereoisomeric adducts, (R, S)- and (S, S)-N-(2-hydroxy-2-methyl-3-buten-1-yl)-l-valine methyl ester, from S_N2 attack of the valine amino solely at C-3. Reactions of rac.-2-ethenyl-2-methyloxirane with cysteine derivatives occurred at C-2 in neutral polar media (S_N1 reaction) or at C-3 in basic media (S_N2), whereas for ethenyloxirane products arose from attack at both C-2 and C-3. Reaction of meso-butadiene diepoxide (meso-2,2'-bioxirane) with l-valine methyl ester gave mainly 2:1 adducts, dimethyl 2,2'-(((2R,3S)-2,3-dihydroxybutane-1,4-diyl)bis(azanediyl))-(2S,2'S)-bis(3-methyl-butanoates), whereas 2-methyl-2,2'-bioxirane gave a mixture of 1:1 [methyl 2-(3,4-dihydroxy-3-methylpyrrolidin-1-yl)-3-methylbutanoates] and 2:1 adducts. Meso-2,2'-bioxirane reacted with N-acetylcysteine methyl ester in methanol to afford meso-thiolane-3,4-diol, by elimination of N-acetyldehydroalanine methyl ester from a precursor cyclic adduct. Similarly, 2-methyl-2,2'-bioxirane gave solely 3-methylthiolane-3,4-diols. Thus, the methyl group of isoprene has a subtle effect on the reactivity of its epoxides relative to those of butadiene and therefore, in the context of their toxicology, could abrogate crosslinking of nitrogen functions in biomolecules related to mutagenicity and carcinogenicity.

Preparation of (mono)sulfonates: Suitable precursors for unnatural sulfonolipids

Aiming at the preparation of the novel unnatural, non-isosteric sulfonolipids bearing one, two and three acyl groups 8, 9 and 10, their precursors hydroxyl-containing sulfonates have been prepared from a variety of hydroxyl-containing halogenides and epoxides using the Strecker reaction. Thus, the sulfonates 16 and 22 were prepared pure, while the sulfonate 27 could only be prepared as a by-product using 1,4-dibromo-2,3-butanediol 26 and in low yields. For these reactions, probable pathways leading to the isolated or spectroscopically identified products are proposed. Conclusions about the relative nucleophilicity of SO32- compared to AsO33 - (as well as HO- which is present in their aqueous solutions) were drawn based on the yields of the corresponding arsonic acids and sodium sulfonates. The IR (KBr) and 1H NMR (D2O) spectra of sulfonates (and in some cases of their sulfonic acids) are analyzed and discussed.

Practical Approach to α- or γ-Heterosubstituted Enoic Acids

The reaction of alkenyl trichloromethyl carbinols with various nucleophiles under protic basic conditions reveals that mercaptans participate by alpha-substitution (S(N)2) of the intermediate alkenyl gem-dichloroepoxides. Conversely, hydroxide results in preferential gamma-substitution with stereoselective allylic transposition (S(N)2'). Regioselectivity with alkoxides depends upon the level of alkene substitution. [reaction: see text]

Regio- and stereoselectivity of the addition of O-, S-, N-, and C-nucleophiles to the beta vinyl oxirane derived from D-glucal

6-O-Trityl- (1a) and 6-(O-benzyl)-substituted epoxide (1b) derived from D-glucal were examined in their addition reactions with O-, C-, N-, and S-nucleophiles. A 1,4-regio- and beta-stereoselective or an anti 1,2-addition pathway is commonly observed depending on the ability of the nucleophile to coordinate with the oxirane oxygen. When TMSN(3) or LiN(3) are used as azide-based nucleophiles, a 1,2-syn-addition pathway is also observed.

Regioselective and divergent opening of vinyl epoxides with ethoxyacetylene

A divergent protocol for nucleophilic opening of vinyl epoxides with ethoxyacetylide has been developed and demonstrated to give complete regioselectivity depending on reaction conditions.

Asymmetric Aminolysis of Aromatic Epoxides: A Facile Catalytic Enantioselective Synthesis of anti-β-Amino Alcohols

[reaction: see text] The first asymmetric aminolysis of trans-aromatic epoxides with anilines is described. The process affords enantioenriched anti-beta-amino alcohols in up to 99% ee. The complete regio- and diastereoselectivity observed uses commercially available [Cr(Salen)Cl] as a Lewis acid catalyst and in combination with a very simple experimental procedure renders the present reaction a facile and practical tool for the synthesis of chiral nonracemic anti-beta-amino alcohols.

A regio- and stereodivergent route to all isomers of vic-amino alcohols

Vicinal amino alcohols are substructures in several important natural products. They are also frequently employed ligands in asymmetric synthesis. Many enantioselective syntheses of vic-amino alcohols have been reported, but each structure has required its own synthetic route. This study presents a synthetic strategy leading to all eight possible isomers of a given beta-amino alcohol, starting from vinyl epoxides. The developed strategy focuses on the propensity of vinyl epoxides and vinylaziridines to be selectively ring-opened at the allylic position by suitable hard nucleophiles. Within this strategy, a novel large-scale aminolysis reaction and the synthesis of a trisubstituted N-H vinylaziridine are detailed.

A regio- and stereodivergent synthesis of vic-amino alcohols

A regio- and stereodivergent synthesis of vic-amino alcohols starting from vinylepoxides is described. The developed strategy focuses on the propensity of vinylepoxides and vinylaziridines to be ring-opened at the allylic position by suitable nucleophiles and makes use of reactions that perform such tasks selectively with either retention or inversion of configuration.

Studies on the molecular toxicology of buta-1,3-diene and isoprene epoxides

Reactions of ethenyloxirane with amino (RNH2) and thiol (R'SH) nucleophiles occur by an SN2 mechanism involving competing ring cleavage at C-2 and C-3. In contrast, 2-ethenyl-2-methyloxirane reacts with amino (RNH2) and thiolate (R'S-) nucleophiles in methanol by regioselective SN2 attack at C-3 ("neo-pentyl" position). However, in pure water or methanol SN1 reaction occurs mainly at C-2.