Transition metal catalyzed allene substrates catalysts

Hydroalkoxylation of Allenes In the year 2000, during their investigation of transition metal catalyzed reactions of allenyl ketones [29], Hashmi et al. discovered that gold(III) salts were able to lead the cydoisomerization and dimerization of these substrates (Equation 8.2) with a considerable improvement related to other assays with Ag (I) or Pd (II) catalysts [18]. 

Transition metal catalyzed intramolecular [4+2] diene-allene cycloadditions provide 6,6- and 6,5-fused ring systems in good yields under mild conditions. For example, from the tethered allene 404 in the presence of Ni(COD)2 as the catalyst a 97 % yield of the cycloadduct 405 is obtained resulting from addition to the terminal allene double bond. From the same substrate, using [Rh(COD)Cl]2 as the catalyst, the hydrindane derivative 406 is obtained in 90 % yield. 

From the results presented here, one could get the impression that such allenes with hydroxyl groups in the substituents will always form heterocydes in the presence of transition metal catalysts, but in the presence of other substrates even allenylcarbinols can react to give different products. Examples are the rhodium-catalyzed reaction of allenylcarbinol 78 and phenylacetylene 79 to 80 [42], the palladium-catalyzed reaction of 81 and pyrrolidine 82 to 83 [43] and the ruthenium-catalyzed reaction of 78 and 79 to 84, an isomer of the rhodium-catalyzed reaction of the same substrates mentioned above [44] (Scheme 15.19). 

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