[itsmequinn]

Yes, but then he won't have to pay additional capital gains tax on the stock if it happens to skyrocket in the years following his renunciation of citizenship. You only pay tax on the profit you make on stock investments, so any profit he stands to make in the years following his renunciation will be tax free.

[sp332]

Any profit he stands to make in the years following will be taxed according to the laws of his new residence.

[xiaoma]

As itsmequinn said, tax free.

http://en.wikipedia.org/wiki/Capital_gains_tax#Singapore

[sses]

Yes but they won't be US taxes, which are the only taxes US immigration law cares about in this context. He's still avoiding US taxes.