Morphanthridizinium salts

The insertion of allenes in the palladium-carbon a bond of cyclopalladated pyridine derivative 295 (cf. 00CRV3067) affords stable, isolable (ry -allyl) palladium complexes (e.g., 296) (03JOM(687)313). The ideally located imine unit when depalladated reacts selectively with the allyl functionality to yield methylene morphanthridizinium salts 297a-c. 

By contrast to the bases, the cationic species have long been known. In addition to Fozard and Jones bicyclic salts already described (307, 308), benzo-fused derivatives were synthesized in the context of the aromatic cyclodehydration series by Bradsher s group (Scheme 71). Different from the 2-propenylpyridinium salts 316 just mentioned, the cycHzation of 2-benzylpyridinium 318 salts does not give indolizines unless under basic conditions in the acidic medium morphanthridizinium salts, such as 319a and b, are formed (59JA2547). This cyclization (after iodo-chloro metathesis) takes place in several days but in the case of the... 

---