var raster = new ol.layer.Tile({
  source: new ol.source.OSM()
});

var wkt = 'POLYGON((10.689 -25.092, 34.595 ' +
    '-20.170, 38.814 -35.639, 13.502 ' +
    '-39.155, 10.689 -25.092))';

var format = new ol.format.WKT();

var feature = format.readFeature(wkt, {
  dataProjection: 'EPSG:4326',
  featureProjection: 'EPSG:3857'
});

var vector = new ol.layer.Vector({
  source: new ol.source.Vector({
    features: [feature]
  })
});

var map = new ol.Map({
  layers: [raster, vector],
  target: 'map',
  view: new ol.View({
    center: [2952104.0199, -3277504.823],
    zoom: 4
  })
});
