Including Thursday's activity, five large inversions have been agreed in 2015 and several more attempts are under way, including Monsanto's $45 billion pursuit of Switzerland's Syngenta.
Advisers said that the appetite for inversions has been at fever pitch again in recent months, as the Obama administration failed to gather congressional support to pass legislation intended to further stymie these deals with important tax components.
Frank Aquila, a partner at Sullivan & Cromwell, said: "US companies will continue to seek opportunities to level the playing field until Congress and the president recognise that the US tax code disadvantages US businesses."
Dealmakers believe more large inversion deals are coming, given the reluctance of a Republican majority in Congress to clamp down on deals without an agreement for broader tax reform.
Christopher Cox, chairman of the corporate practice at law firm Cadwalader, Wickersham & Taft, said companies were still able to navigate the Treasury actions to complete beneficial inversions.
"The new regulations removed the benefits of so-called 'hopscotch' loans, which allow trapped offshore cash to be used to finance inversion transactions," said Mr Cox. "But the door to do tax inversions is still wide open and for many companies it is still a very effective way to cut tax costs."
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The Treasury pledged last year to introduce a second round of anti-inversion measures and a spokeswoman said on Thursday: "We are continuing to review a broad range of authorities for further anti-inversion measures to close loopholes that permit some taxpayers to avoid paying their fair share of taxes and we expect to issue additional guidance to further limit inversion transactions in due course."
The revival in inversions is helping to accelerate the pace of dealmaking since inverted companies have tax advantages over their non-inverted US rivals when seeking further acquisitions.
Foreign-domiciled companies have spent $315 billion since January to buy US-domiciled targets, according to S&P Capital IQ, close to the record for the whole of 2007, the previous peak.
Many of these acquirers have been assisted by a lower tax rate, allowing them to compete more aggressively against would-be US acquirers. That is putting pressure on US companies, who complain that the US tax code is hurting their ability to compete globally.