The turning point for Stephan Jung came in February, around the time bonus checks were slashed. A veteran of UBS, one of many banks tarnished by the financial crisis, Mr. Jung realized that the old Wall Street would not be bouncing back any time soon. It was time to head for the new.

“After 10 years, I did not see a future for myself,” said Mr. Jung, 42, who quit to parlay his sales expertise into a career at Aladdin Capital, a small but rising investment firm run by others who had also left some of the most venerable names in finance.

There is an air of exodus on Wall Street  and not just among those being fired. As Washington cracks down on compensation and tightens regulation of banks, a brain drain is occurring at some of the biggest ones. They are some of the same banks blamed for setting off the worst downturn since the Depression.

Top bankers have been leaving Goldman Sachs, Morgan Stanley, Citigroup and others in rising numbers to join banks that do not face tighter regulation, including foreign banks, or start-up companies eager to build themselves into tomorrow’s financial powerhouses. Others are leaving because of culture clashes at merging companies, like Bank of America and Merrill Lynch, and still others are simply retiring early.