Male cat is very vocal. How do I stop him from bellowing to go outside when he can't?

On days that he can't go out provide him with some catnip toys and a scratching post to play with and divert his attention. Just like dogs, cats can become bored without sensory stimulation, and that's when they get into trouble. Punishing him by isolating him on the porch will not stop him from yowling it will only contribute to his boredom and perhaps increase his vocalizations.