<div class="form-horizontal">
      <label class="required-inputs"><b>Descrição</b></label>
      <select id="select2-ex" name="state" style="width: 100%;">
           @foreach($professores as $p)
                <option value="{{$p->id}}">{{$p->nome}}</option>
           @endforeach
       </select></div>

$(document).ready(function() {
    $('#select2-ex').select2();
});