Hello Carlos,
the best way to export cinema 4D video to after effects is to render your Cinema 4D animation as a PNG. Make sure to render all the frames. This way you’ll have a folder with alot of PNG files. (the many frames your animation has). Now you can create a png sequence in Adobe Premiere and export that as an Alpha quicktime video file. Hope this will help you out! If you dont get it or got any questions. In my latest video on Youtube I’m also exporting my project as with an alpha channel. Search ‘Detline’ on youtube and you’ll find it 😉