Hydroamination, Hydrocarbonation, and Related Reactions

Addition of C, N, and 0-pronucleophiles to alkynes is catalyzed by Pd complexes. Pd-catalyzed hydroamination of alkynes is rare. Intramolecular hydroamination of 6-amino-1-hexyne (44) was catalyzed by a Pd(II) compound and 2-methyl-1,2-dehydropiperidine (46) was obtained as a final product via 2-methylenepiperidine 45 [13]. 

1-Phenyl-1-propyne (55) underwent facile formal intermolecular hydroamination, affording the allylic amine 56 in high yield at 0 C in the presence of AcOH or benzoic acid. In this reaction, at first, Pd-catalyzed isomerization of 55 to pheny-lallene (57) occurs by addition-elimination of H-Pd-OAc to internal alkyne 55, and then the allene 57 is converted to jr-allylpalladium intermediate 58 by hydropal-ladation. The final step is a well-known amination to produce the allylic amine 56. As an intramolecular version, 2-(2-phenylpropenyl)pyrrole (60) was obtained from l-phenyl-7-amino-l-hexyne 59 [16,16a]. Similarly Pd/benzoic acid-catalyzed hydroalkoxylation of 55 with (—)-menthol (61) afforded the allylic ether 62 [17]. 

Conjugated enynes are very reactive and show interesting reactivity in the presence of Pd catalysts. Hydroamination of the conjugated enyne 71 in the presence of AcOH afforded 1,4-diamino-2-butene 72. In this reaction, Pd-catalyzed isomerization of the enyne to allene, followed by generation of the methylene-TT-allylpalladium 73 occurs, and amination yields the allenylamine 74. Further Pd-catalyzed amination of 74 affords the diamine 72. The reaction took place in the presence of AcOH using DPPF as a ligand [20]. A similar reaction occurred with carbon pronucleophiles [21]. 

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