In angular2@2.0.0-alpha.48:

facade/async.js line 19 calls require('rxjs/operators/toPromise');

As of rxjs@5.0.0-alpha.12 this folder was renamed to operator/toPromise.js.

The result is that a jspm install of angular 2 without bundling gets the following error:

GET http://localhost:8080/jspm_packages/npm/rxjs@5.0.0-alpha.12/operators/toPromise.js 404 (Not Found)

The rxjs version should either fixed at version alpha.10 or this reference udpated to operator/toPromise.js