Try:
var myMap; // global variable representing the map
require([
"dijit.layout.BorderContainer",
"dijit.layout.ContentPane",
"dijit.layout.AccordionContainer",
"esri.map",
"esri.geometry.Extent",
"esri/layers/ArcGISTiledMapServiceLayer",
"esri/layers/ArcGISDynamicMapServiceLayer",
"dojo/domReady!"
], function(BorderContainer, ContentPane, AccordionContainer, Map, Extent, ArcGISTiledMapServiceLayer, ArcGISDynamicMapServiceLayer) {
var initialExtent = new Extent({"xmin":-13050590.679808607,"ymin":3848824.1306140213,"xmax":-13033430.566958608,"ymax":3863366.2752452563,"spatialReference":{"wkid":102100}});
myMap = new Map("mapDiv", {extent:initialExtent});
var baseLayer = new ArcGISTiledMapServiceLayer("http://services.arcgisonline.com/ArcGIS/rest/services/World_Street_Map/MapServer");
var opLayer1 = new ArcGISDynamicMapServiceLayer("http://sampleserver6.arcgisonline.com/arcgis/rest/services/NetworkAnalysis/SanDiego/MapServer",{ opacity:0.8 });
myMap.addLayers([baseLayer, opLayer1]);
});