Addition to Conjugated Enynes and Related Reactions

For the selective 1,4-hydrosilylation to 133 giving the allenic product 134, the presence and orientation of the two -SiMe3 groups at the 1- and 4-positions in 133 play important roles. Reaction of the hydrosilanes with the closely related conjugated enynes 136 and 137 in the presence of the Pt or Rh catalyst proceeded in a 1,2-addi-tion manner to produce conjugated dienes instead of allenes [108], 

132n [Si] = SiEt3 132p [Si] = SiMe2Ph 132r [Si] = SiMePh2 

150a 73% (83% selectivity) 150b 74% (88% selectivity) 150c 89% (83% selectivity) 

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