 Silicon @-@ directed Nazarov cyclizations can exhibit induced diastereoselectivity in this way . In the example below , the silyl @-@ group acts to direct the cyclization by preventing the distant alkene from rotating " towards " it via unfavorable steric interaction . In this way the silicon acts as a traceless auxiliary . ( The starting material is not enantiopure but the retention of enantiomeric excess suggests that the auxiliary directs the cyclization . ) 
