[rudiger]

Here's how he's avoiding taxes:

He's making this move before Facebook is public.

Once Facebook is public, the value of his stake is much more transparent (and harder to fool around with). In your first example, the valuation of a privately-held company determines the exit tax. In your second example, Facebook is a public company and its valuation is determined by a public market. Singapore has no capital gains tax, so if he exits now with the lower private company valuation, he won't pay taxes on the difference.