text:  An <unk> is an organic molecule that features a three @-@ membered <unk> containing oxygen , nitrogen , and carbon . In their largest application , <unk> are <unk> in the industrial production of <unk> . <unk> derivatives are also used as specialized reagents in organic chemistry for a variety of <unk> , including alpha <unk> of <unk> , <unk> and <unk> of <unk> , and other <unk> transfer reactions . <unk> also serve as precursors to <unk> and participate in [ 3 + 2 ] <unk> with various <unk> to form substituted five @-@ membered <unk> . <unk> <unk> derivatives effect asymmetric oxygen transfer to <unk> <unk> as well as other substrates . Some <unk> also have the property of a high barrier to <unk> of the nitrogen , allowing for the possibility of <unk> at the nitrogen center . 
  