There are several possible ways.
In case your editor with "id1" is the active Editor:
tinymce.activeEditor.execCommand('mceInsertContent', false, 'your content');
In case you want to use the id:
tinymce.get("id1").execCommand('mceInsertContent', false, 'your content');
In case you only have two editors and your editor with "id1" has been initialized first:
tinymce.editors[0].execCommand('mceInsertContent', false, 'your content');