Aminoallene intermediates

Clavepictines A and B were prepared using a variety of effective reactions on the piperidine ring, such as a silver-promoted cyclization of an aminoallene intermediate, diastereoselective alkylation, and cross coupling of an enol triflate <99JA10012>. 

When allene derivatives are treated with aryl halides in the presence of Pd(0), the aryl group is introduced to the central carbon by insertion of one of the allenic bonds to form the 7r-allylpalladium intermediate 271, which is attacked further by amine to give the allylic amine 272. A good ligand for the reaction is dppe[182]. Intramolecular reaction of the 7-aminoallene 273 affords the pyrrolidine derivative 274[183]. 

Cyclizations with nitrogen nucleophiles involving alkynes and allenes have received little attention until recently. The cyclizations of several a-aminoallenes to 3-pyrrolines with silver tetrafluoroborate was reported by Claesson and coworkers (equation 133).264 A similar cyclization to form A -carba-penems has been reported (equation 134).265 Diastereomeric allenes (R1 R2) were shown to cyclize with complete stereocontrol. Cyclization with palladium chloride in the presence of allyl bromide or electrophilic alkenes allowed for the intermediate vinylpalladium species to be trapped by the electrophile.2651 A related product was obtained by cyclization of an alkynic substrate (equation 13S).265 Other examples of 5-endo cyclization of p-aminoalkynes50 include the formation of indoles by cyclization of 2-alkynylanilines with mercury salts200 or palladium chloride,266a,266b,266c formation of 1-pyrrolines with catalytic palladium chloride (equation 136)198 and formation of pyrroles by cyclization of hydroxy-substituted p-aminoalkynes.198,2666... 

Type 4 metallocene complexes catalyze the regioselective mtermolecular addition of primary amines to acetylenic, olefinic, and diene substrates at rates which are = 1/1000 those of the most rapid intramolecular analogues [165]. Variants such as the intramolecular hydroamination/cyclization of aminoallenes [166] and the intra- and intermolecular tandem C-N and C-C bond-forming processes of aminodialkenes, aminodialkynes, aminoallenynes, and aminoalkynes [167] were applied as new regio- and stereoselective approaches to naturally occurring alkaloids. For example, bicyclic pyrrolizidine intermediate E... 

Tetrasubstituted imidazoles have been prepared from propargyl amines, sulfonyl azides, and terminal alkynes A-sulfonyl ketenimine and aminoallene are reported to be the key intermediates for the two-step one-pot transformation (Scheme 183). " ... 

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