The alchemists of Wall Street are at it again.

The banks that created risky amalgams of mortgages and loans during the boom — the kind that went so wrong during the bust — are busily reviving the same types of investments that many thought were gone for good. Once more, arcane-sounding financial products like collateralized debt obligations are being minted on Wall Street.

The revival partly reflects the same investor optimism that has lifted the stock market to new heights. With the real estate market and the economy improving, another financial crisis seems a distant prospect. What’s more, at a time when the Federal Reserve has pushed interest rates close to zero, the safest of these new investments offer interest rates almost double that paid by ultrasafe United States Treasury securities, according to RBS Securities, which was involved in such instruments in the past.

But the revival also underscores how these investments, known as structured financial products, have largely escaped new regulations that were supposed to prevent a repeat of the last financial crisis.

“All of this seems like a fairly quick round trip,” said Manus Clancy, a managing director at Trepp, a research firm that focuses on commercial real estate. “You are seeing a fair number of sins being forgiven.”