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Die 0x0-iminiumsalze I l a -e und 13a -e werden durch Oximierung der w-Chlorketone 9a -e iiber die cyclischen Oximether 10a -e bzw. die cyclischen Imin-oxide 12a -e und deren anschlienende Alkylierung mit ,,Meerweinsalr" hergestellt. Die Deprotonierungsreaktionen von 11 a -e sowie 13a-e fiihren uber die regioselektiv hergesiellten Zwischenprodukte 14a-e bzw. 17a-e zu den a,p-ungesattigten lminen 15a -e und den cyclischen lminen 18a -e. Synthesis and Thermolysis of 0-Alkyl-N-vinylhydroxylamine DerivativesOxoiminium salts l l a -e and 13a-e have been prepared from the o-chloroketones 9 a -e by oximation via the cyclic oxime ethers 10a-e and the cyclic imine oxides 12a-e, followed by alkylation with ,,Meerwein salt". The deprotonation reaction of 11 a -e and 13a -e yields, uiu the regioselectively prepared intermediates 14a -e and 17a -e, the a$-unsaturated imines 15a -e and the cyclic imines 18a-e, respectively.In Fortfuhrung unserer Untersuchungen uber 0x0-iminiumsalze') bemiihten wir uns urn die Synthese sowie die chemischen Anwendungsm6glichkeiten der bisher nur wenig untersuchten N-Vinyl-O-alkylhydroxylamine2'.

Penetration of the blood brain barrier (BBB) by appropriate fluorescent probes remains a challenge in optical imaging and diagnostics. We designed, synthesized and observed the in vivo BBB penetration of a LASER syn-bimane probe. Results demonstrate that the Aib transporter unit in our probe may lead a fluorescent bimanyl moiety across the BBB.

The oxoiminium salts 4a, b, and 8 obtained by alkylation with Et30BF4 of the aldonitrones 3a, b, and 7 react with diphenyl hydrogen phosphite to give the N-alkoxy a-amino phosphonic esters 6 and 9a, b. Similarly, the cyclic imine oxides lOa, b and the cyclic oxime ethers 14a, b afford the a-branched N-alkoxy a-amino phosphonic esters 12a, b and 16a, b, respectively. Hydrogenolysis and ester hydrolysis affords the a-methyl a-amino phosphonic acid hydrochlorides 13 a, b and 17a. b.Oxoiminium salts 1 are central synthetic intermediates in several preparative methods. Examples are the cycloaddition of a-chloronitrones') and a-bromo oxime ethers') to olefinic'") and acetyleniclb) systems. However, 1 can also be synthesized by direct 0-alkylation of nitrones 3, or N-alkylation of oxime ethers3). A characteristic feature of these reactive synthetic intermediates is the ability to add various nucleophiles to the C = N bond system in 1 to give the products 2a-c efficiently. The amino nitriles 2c are of particular interest for amino acid synthesis, as they open a potential entrance to a variety of new unnatural amio acids4).In this paper we would like to report on the reactions of some oxoiminium salts with the phosphorous derivative6), diphenyl hydrogen phosphite (HP03Ph2, 5)7), and the transformation of the resulting N-alkoxy a-amino phosphonic esters into a-branched a-amino phosphonic acid^^,^).Ethylation of benzaldehyde N-methylnitrone (3a) and pyrroline N-oxide (3 b) with triethyloxonium tetrafluoroborate (Meerwein's salt) in CH2C12 for 18 hours at room temperature, followed by reaction of 4a, b with HP03Ph2 (5) for an additional 3 hours at room temperature gave 6a and 6b in 72 and 70% yield, respectively. Similarly, reaction of the chiral nitrone 7") with Meerwein's salt in CH3CN, followed by reaction of 8 with 5, afforded a 3:2 mixture of the two stereoisomers of 9. This mixture was then separated by A1203 chromatography into its two diastereomeric components 11J2).It is apparent that the reaction of 8 with 5 is enantioselective, producing unequal amounts of 9a and 9b. From considerations of least hindrance in approach of the reagent and minimum crowding in the transition state, we assume that attack of 8 by HP03Ph2 might be favored from the si side, to yield 9a preferentiallyi3). Attempts to form the alkali metal salts (Li, Na)14) of both a-amino phosphanic esters 6a, b and 9, and subequently to methylate the salts failed. We therefore approached the synthesis of 13a and 13b from the nitrones 10a and lob, respectively. 0-Benzylation of 10a (benzyl iodide in CH3CN) afforded the oxoiminium salt l l a . Reaction with 5 gave the corresponding a-methyl N-ethoxy amino phosphonic ester 12a in 82%. Ethylation of 10b (Et30BF4 in CH,C12) provided the oxoiminium salt llb3). Addition of 5 afforded 12b in 78% yield. Hydrogenolysis of the N -0 bond (H2/10%

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