Angular bootstrap dropdown-toggle not working

Question

Add a css class dynamically: In my angular application, I am using bootstap dropdown,dropdown-toggle to display drop down on click of a button. But the drop down is not shown and the class is not appended by additional property.

On click of 'My List', I need to display a list which shows View Emp Details, View Address Details. On click, should become which is not happening, Am I missing anything, I tried using [ngClass] still doesn't work. Below is the code:

<div class="nav-wrapper" >
     <ul class="nav nav-tabs" >
       <li  class="dropdown" dropdown >
            <a class="dropdown-toggle" data-toggle="dropdown" dropdownToggle role="button" >My List<span class="caret"></span></a>
                <ul class="dropdown-menu" role="menu">
                    <li role="presentation"><a  role="menuitem"  [routerLink]="['/abc']" >View Emp Details</a></li>
                    <li role="presentation"><a  role="menuitem"  [routerLink]="['/def']" >View Address Details</a></li>          
                </ul>       
       </li> 
     <ul>
<div>