Nitrosoalkene 2 generated in situ from oxime 3 underwent smooth hetero Diels-Alder reaction with enol ethers 1 to afford 1,2-oxazine derivatives 4 bearing an exocyclic C=C bond. Methoxyallene 8 and 2 provided 6H-1,2-oxazine 10 in good overall yield. The exocyclic double bond of this type of 1,2-oxazines can be employed for addition reactions as demonstrated by dihydroxylation of 4a with potassium permanganate, smoothly delivering 1,2-diol 11. A reductive cascade reaction involving ring cleavage at the N-O bond followed by cyclization steps furnished pyrrolizidinone derivatives 12 in good yields. In the case of 12b this transformation proceeded with excellent stereoselectivity. Finally, the lactam moiety of 12 could be reduced with borane to provide the corresponding pyrrolizidine derivatives 19 in good yield.A common strategy for the construction of functionalized heterocyclic compounds involves ring contraction of easily available precursor heterocycles. For this purpose, a moiety allowing smooth ring opening is required, a property which is given with the relatively weak N-O bond. 2 The compound class of 1,2-oxazines fulfils this prerequisite and hence it is frequently employed in organic synthesis. 3 Ring cleavages and ring transformations could be exploited for the synthesis of a variety of nitrogen-containing heterocycles such as pyrroles, 4 proline derivatives, 4f,5 pyrrolidines, 6 cyclic five-membered nitrones, 4i,5a,7 aziridines, 8 g-lactams, 4i,9 pyridines, 10 and indolizidines. 11 To date, not much is known about the preparation of pyrrolidizines starting from 1,2-oxazine derivatives. 12 The pyrrolizidine core is found in many alkaloids including examples with interesting pharmacological activity. 13 Polyhydroxylated pyrrolidizine alkaloids are of particular importance as inhibitors of glycosidases and glycosyltransferases. 14 The present report deals with the preparation of methyl (E)-3-[1,2-oxazin-3-yl]propenoates and their simple transformation into pyrrolizidinone and pyrrolizidine derivatives.1,2-Oxazines 4 with an exocyclic C=C bond at position 3 can easily be prepared by hetero Diels-Alder reaction of electron-rich olefins 1 and nitrosoalkene 2, which are generated in situ from the corresponding a-bromooxime 3 by treatment with a base such as sodium carbonate (Scheme 1). 15 Cycloadducts 4 were generally obtained in moderate to excellent yields. Dienophile 1c was used as an E/Z mixture of isomers (60:40), however, only the more reactive E-isomer underwent cycloaddition with 2 providing 4c in good yield and with trans-orientated trimethylsiloxy groups. The high kinetic preference for Econfigured dienophiles is a common feature of nitrosoalkene cycloadditions. 16

On the Synthesis of 3‐Amino‐pyrroles by Thorpe‐Ziegler‐Cyclization N‐Aryl and alkylaminomethylene cyanacetic acid derivatives 1 react with α‐halogencarbonyl compounds 2 in the presence of potassium carbonate/sodium ethoxide to yield the substituted 3‐amino‐pyrroles 6. Using the same principle of cyclization pyrrole derivatives 6 can also be obtained by reaction of β‐chloro‐ and β‐alkoxymethylenemalononitriles 4 with β‐aminocarbonyl compounds 5. From the malononitrile derivatives 1 containing the methylthio group in the β‐position, and α‐halogen ketones 7, the 2‐dicyanomethylene oxazolines 8 arise which undergo alkoholysis by treatment with sodium alkoxide to form the 3‐amino‐5‐alkoxy‐pyrrole derivatives 9.

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