Reductive benzylization

The corresponding benzylic reductive cleavage was carried out using aryl-substituted 1,3-dioxanes 419, lithium and a catalytic amount of naphthalene (10%) in THF at temperatures ranging from —78 to —40°C. The obtained benzylic intermediates 420 were then treated with different electrophiles giving, after hydrolysis, the corresponding products 421 (Scheme 118) 3,i94... 

Racemisation of (-)-norreticuline has been accomplished by aromatisation of the tetrahydroisoquinoline system, N-benzylation, reduction of the isoquinolinium salt, and reductive N-debenzylation. Aryloxy radical intermediates arising from both phenolic rings... 

The electrolytic oxidation of the sodium salt of (+ )-N-ethoxycarbonyl-Al-norarmepavine (46) led to the dimeric mixtures (47) and (48). The latter mixture was converted into a mixture of dauricine analogues (49) via O-benzylation, reduction with lithium aluminium hydride, and hydrogenolytic debenzylation. This transformation represents the first preparation of an analogue of a natural bis-benzylisoquinoline by oxidation of a phenolic monomeric benzylisoquinoline. Detailed studies on the mass-spectral cleavage patterns of bisbenzylisoquinolines have appeared. 

The synthesis of enantiomerically pure a-N,N-dibenzylamino aldehydes, e.g. (S)-2-(N,N-dibenzylamino)-3-phenylpropanal prepared from t-Phe-OH by N- and O-benzylation, reduction of the ester to the alcohol, and Swern oxidation, has been described [1389]. 

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