Grunt: Globbing pattern won't work – why?

Question

This is my current Gruntfile:

module.exports = function(grunt) {
  grunt.config.init({
    sass: {
      dist: {
        options: {
          'style': 'expanded'
        },
        files: {
          'assets/css/style.css': 'src/scss/main.scss'
        }
      }
    }
  });
  require('load-grunt-tasks')(grunt);
}

Running grunt sass:dist from the console compiles main.scss into the given directory.

Now I want to use a globbing pattern because the file may be moved or may gets a new name:

module.exports = function(grunt) {
  grunt.config.init({
    sass: {
      dist: {
        options: {
          'style': 'expanded'
        },
        files: {
          'assets/css/style.css': 'src/**/*.scss'
        }
      }
    }
  });
  require('load-grunt-tasks')(grunt);
}

Now I still get Done, without errors. after running grunt sass:dev, but the css won't get compiled.

Probably the globbing pattern somehow fails, but I don't know why?