Amino-allenes hydroamination/cyclization

It has been proposed that Au-catalyzed asymmetric hydroamination/cyclization of amino-allenes proceeds through a catalytic cycle demonstrated in Scheme 39.3. The chiral Au-complex activates the allenes generating the complex A, which is attacked by nitrogen to form species B. Species B upon protonolysis releases the product and regenerates the catalyst. 

SCHEME 39.3. Mechanism of hydroamination/cyclization of amino-allenes with Au-complexes. ... 

To meet the demand, the compound has been successfully synthesized by hydroamination/ cyclization of amino-allene 13" ° (Scheme 39.7). Enantio-selective addition of n-dibutyl zinc to allenyl aldehyde 10 using a chiral Ti catalyst (generated by heating the mixture of 11 and Ti(Ot-Pr)4 in dry toluene at 40-45 °C for 30 minutes) provides the corresponding hydroxyl... 

Hydroamination of Allenes Different related amines can also be cyclized. The use of free amino groups led to long reaction times (several days), but sulfonamides, acetyl or BOc as protecting group led to fast conversion (in the latter case, problems of diastereoselectivity were observed). Optimization studies showed that, although cationic gold (I) complexes were not effective for these conversions, AuCI was a very good catalyst for these reactions. 

---