Retro-Strecker reaction

All attempts [heating with or without a base such as NaOH, potassium carbonate (K2CO3) or DBU] to effect cyclization of a-amino nitriles 52a and 52b to bicyclic compound 58 failed possibly due to such side reactions as those initiated by retro Strecker reaction (Fig. (23)). The compounds 52a and 52 b were thus converted to amides 59a and 59b before the ring closure (Fig. (24)). 

The absence of any bicyclic compound 58 or 53 in the reaction mixture may result from the selective decomposition of anti-SZh through retro Strecker reaction,... 

Since there is great interest in compounds bearing quaternary stereocenters, soluble catalyst 25 was also applied to keto-imines in the presence of in situ generated HCN (Scheme 30.6) [17]. Whereas hydrocyanation adducts of N-allyl protected ketimines were prone to decompose via a retro-Strecker reaction, N-benzylated Strecker adducts 28 were obtained in mostly excellent yields and very high ee s. In general, acetophenone imines 27 were suitable substrates whereas aliphatic ketimines 27 showed a lowered optical purity. Although the benzyl protection group was necessary to obtain stable Strecker adducts 28, transformation of these adducts into amino acids was made more difficult. It could also be shown that... 

The second method, referred to as the decarbonylation reaction, concerns a base-catalyzed elimination of HC1 and CO from an acid chloride.31 The amide moiety was converted into the amino acid 15 by reaction with Na202 in water.32 Alternatively, amides can be converted into the corresponding carboxylic acid by treatment with concentrated HC1.33 However, this method produced lower yields as a result of some decomposition. The carboxylic acid 15 was treated with the Vilsmeier reagent and triethylamine furnishing the imine 16 via decarbonylation. The imine 16 was then converted, in a similar manner to the retro-Strecker method, to the unprotected homoall-ylamine 17 in 75% overall yield and an ee of 98%. 

DKR of A/-methyl a-aminoni-triles in which the racemization took place via the lipase-catalyzed retro-Strecker and Strecker reaction. 

By retro-aldol cleavages of the 1-deoxyosone short-chain dicarbonyls like diacetyl, methylglyoxal or hydroxydiacetyl are formed which - like the deoxyosones - may participate in the Strecker degradation of amino acids, thus creating volatile flavor components 17,18). On the other hand, the 1-deoxyosone undeigoes several cyclization reactions yielding e.g. acetylfiiran, maltol, isomaltol, furaneol and 5-hydroxy-5,6-dihydromaltol (DHM) (75). 

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