Synthesis and Structure of Heterocumulenes with and Units

Preparations, IR and NMR spectra of 1‐oxa‐3‐azabutatrienium hexachloroantimonates ( 2a – f ) and of 1‐thia‐3‐azabutatrienium hexachloroantimonate 2g are reported. According to an X ‐ray structure analysis of 2b , g these compounds crystallize as pseudocumulenes with bent C=N=C=X units ( C=N=C 129° for X = O and 139° for X = S). The extremely moisture sensitive salts 2a – e react with water to give the iminium salts 3 , while 2g gives benzophenone. With carboxylic acids the 1‐oxabutatrienium salts 2a – e afford carboxylic anhydrides (e.g. 4 ) and the iminium salts 3a – e . The α‐naphthyl compound 2c cyclizes to give the isoquinolinium salt 5 . With N , N ‐dimethylaniline 2a , e , g afford triarylcarbenium dyes ( 8 ).