Punitive measures do not work for children with Aspergers Syndrome.  They usually serve to frustrate the child and contribute to eroding his/her self-esteem. 

Giving "ultimatums" also does not work. 

Whenever possible, teach the rationale behind why he/she is expected to behave a certain way.  Assume nothing.  Children with Aspergers often lack the intuitive understanding as to what is "expected" of them.  Likewise, they often lack the repertoire of socially appropriate things to say and do in a variety of social contexts. 

Situations that would dictate a "time-out" for a typical child are usually opportunities to teach social skills to the Asperger child.