Reactions of Heteroaryliminotriphenylphosphoranes with Heterocumulenes: Synthesis and Cycloaddition Reactions of α‐N‐Heteroaryl‐substituted Carbodiimides
N‐α‐Heteroaryl‐substituted iminotriphenylphosphoranes react with phenylisocyanate, phenylisothiocyanate, and carbon disulfide to symmetrical and unsymmetrical α‐heteroaryl‐carbodiimides. These can not be isolated as monomeres because they behave as 1.3‐diazabutadienes predominantly and form 4+2‐cycloadducts. The monomeric intermediates cyclodimerize to the 1.3.5‐triazines 5 resp. 14 or react by the same scheme both with phenylisocyanate and with phenylisothiocyanate to give the 1.3.5‐triazines 4, resp. 12. In competition with this reaction a 2+2‐cycloaddition takes place, hence there follow numerous by‐products. The structure of 1.3.5‐triazines is determined from hydrolysis to guanidines 6 and on the basis of spectroscopic methods.
Partial Syntheses of Cardenolides and Cardenolide Analogues. XIII. Synthesis of Substituted 14,21‐Epoxy‐5β,14β‐card‐20(22)‐enolideThe 12‐substituted 14,21‐epoxy‐5β,14β‐card‐20(22)‐enolides 3 and 5 were synthesized by oxidation of the appropriate 17β‐(3‐furyl) derivatives 2b and 2c, respectively, with chromic acid. 5 was converted to the conjugated Δ9(11)‐12‐ketone 6 by dehydrogenation with selenium dioxide.The biological activities of the new compounds were investigated and are discussed.
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