Umylidierungen von mit R 22BCl im Molverhältnis 2 : 1 ergaben die neuartigen kristallinen Ylide 1, die man auch durch eine mesomere Grenzform 1b mit BC‐Bindung beschreiben kann. Bisher wurde nur mit Halogeniden von Elementen der 4.–7. Hauptgruppe umylidiert.
Transylidation of R1HC⊕P⊕Ph with R 22BCl in the molar ratio 2 : 1 furnished the novel crystalline ylides 1, which can also be described in terms of a mesomeric formulation 1b with BC bonding. Hitherto, transylidations have been carried out only with halides of the 4th—7th main group elements.
The isomerization of N,O-acetals 1 yields N-acyl-0-vinyl amino)aldehydes 3. The relative configurations of the proacetals 2 or 2-aminomethyl-l,3-butadienes 10, depending on ducts 3 have been determined by X-ray analysis and 'Hthe nature of the nitrogen substituents. In the presence of NMR experiments. The mechanism of the reaction is discustrimethylsilyl trifluoromethanesulfonate (TMSOTf) the N,O-sed. Crossover experiments indicate an intermolecular acetals 2h-u are converted stereoselectively into P-(N-acyl-course of the rearrangement. In connection with our investigations of the stereoselective rearrangements of alkyl vinyl a c e t a l~ [~~] to aldol ethers, we have also studied the reactions of 0-vinyl N,O-acetals. In this paper we report on the diastereoselective synthesis of p-(N-acy1amino)aldehydes 3 in three simple steps from easily accessible starting materials via N,O-acetals 1 and 2 (Scheme l)[331. The type of catalyst depends on the nitrogen substituents of the starting materials (Table 2).
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