Partial Synthesis of Meloscine and Scandine

The base 358 is only one of four products obtained when vincadifformine chloroindolenine (295) is allowed to stand with aqueous acetic acid 243). The other products are the corresponding hydroxyindolenine 285 the pen-tacyclic base (362), identical with that obtained earlier by solvolysis of 295 with hot aqueous tetrahydrofuran 244) and a new tetracyclic base, formulated as 3. When heated in acetic anhydride, the chloroindolenine 

Reagents i, AcOH, H2O ii, AcgO iii, AcOH iv, CH2O, NaBHsCN, AcOH 

363 was heated with formaldehyde in acetic acid, the base 365 was obtained in 60% yield (243). 

Which of these two mechanisms is correct depends on the absolute configuration of the product 365. In Lewin s mechanism C-20 suffers inversion, whereas in Ldvy s mechanism C-7 becomes inverted. In consequence, 

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