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Here are five things you must know for Friday, June 21:

1. -- Stock Futures Fall on Report U.S. Planned Air Strike on Iran but Reversed Course

U.S. stock futures declined on Friday following a report that President Donald Trump ordered, and then rescinded, an airstrike on military installations in Iran.

The planned strike, which was reported by The New York Times, was meant to take place early Friday in response to the downing on Thursday of a U.S. drone patrolling the Strait of Hormuz. Trump had warned that Iran made a "big mistake" and warned of consequences to follow, but appeared to pull back from executing a military response only hours before U.S. jets were set to take off.

The Times was unable to determine if Trump merely had postponed the strike, or cancelled it altogether, raising concerns that tensions in the region could quickly escalate. The Federal Aviation Administration issued a warning to carriers in the region not to pass through Gulf of Oman waters and United Airlines (UAL - Get Report) suspended a Newark-bound flight originating from Mumbai.

Contracts tied to the Dow Jones Industrial Average fell 28 points, futures for the S&P 500 were down 5.50 points, and Nasdaq futures declined 27 points.

The S&P 500 closed at a record high Thursday on signals from the Federal Reserve that it was leaning toward interest rate cuts in 2019

Benchmark 10-year bond yields, which traded at a November 2016 low of 1.974% on Thursday, were at 2.035% early Friday.

Gold prices, meanwhile, surged to a six-year high on Friday as investors sought safety from falling global currencies, negative interest rates and the prospect of escalating military tensions in the Gulf region. Spot gold prices hit $1,410.78 an ounce in overnight trading, the highest since September 2013, before paring that advance to around $1,391.10.

The economic calendar in the U.S. for Friday includes the PMI Composite FLASH for June at 9:45 a.m. ET, and Existing Home Sales for May at 10 a.m.

Carmax (KMX - Get Report) is expected to report earnings on Friday.

2. -- Canopy Growth Posts Revenue Beat, Wider Fourth-Quarter Loss

Canopy Growth (CGC - Get Report) posted better-than expected fiscal fourth-quarter revenue but cautioned that its recently approved deal to acquire rights for U.S. based Acreage Holdings (ACRGF) will lead to a charge that will have "a materially negative impact on net income in the first quarter of fiscal 2020."

The Canadian based medical and recreational marijuana grower reported net revenue of CA$94.1 million ($71.4 million) vs. CA$22.8 million ($17.3 million) a year earlier. Analysts had been expecting the company to report revenue of $67.7 million.

The loss in the quarter was C$323.4 million, or 98 cents a share, wider than a year-earlier loss of C$54.4 million. The operational loss in the period, the company said, was C$174.5 million.

Canopy said the average selling price per gram during the quarter fell to CA$7.49 ($5.68) from CA$8.43 ($6.39) a year earlier.

The company said the material non-cash charge it anticipates taking will occur "upon approval of certain modifications of the investor rights agreement with Constellation Brands, as well as terms of existing warrants."

Constellation Brands (STZ - Get Report) took a CA$5 billion ($4 billion) stake in Canopy Growth last year, to help fund the company's expansion in Canada, where marijuana use was legalized last year, and in other countries around the world where restrictions on its use are being relaxed.

Canopy Growth shares declined 6.2% in premarket trading to $41..

3. -- UnitedHealth Reportedly to Buy Payments Processor Equian

UnitedHealth Group  (UNH - Get Report) plans to acquire payments processing company Equian for $3.2 billion, The Wall Street Journal reported.

The health insurer will purchase Equian from private-equity company New Mountain Capital, the Journal reported, citing people familiar with the matter.

Equian provides payment-processing for insurers and healthcare companies and seeks to reduce overpayments, the report said.

Shares of UnitedHealth finished at $247.76 in trading Thursday, down 0.97%, but rose to $248.78 in the after-hours session. 

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4. -- Slack Extends Gains After Its Value Soars in NYSE Debut

Slack Technologies (WORK) shares extended gains in premarket trading Friday, following a direct listing on the New York Stock Exchange Thursday that valued the business-focused software company at $23 billion.

Slack kicked off trading Thursday with a $38.50 opening trade - nearly 50% higher than its reference price of $26 - and closed up 48.5% at $38.62. In premarket trading Friday, the stock was up 3.06% to $39.80.

"Based on our conversations over the past three weeks, investors are very positive overall on Slack and the market opportunity," said D.A. Davidson analyst Rishi Jaluria, who had a $31 price target on the stock ahead of Thursday's listing. "Importantly, investors are believers in Slack's path to profitability, bolstered by best-in-class gross margins and high sales efficiency. Having said that, day one trading should reveal more about investor sentiment and if concerns over revenue deceleration and valuation outweigh the positive viewpoints on the company."

The gains for Slack Thursday came even though a company filing in April revealed it had a $139 million loss for the year ended Jan. 31, on $401 million of revenue. That compares with a year-earlier loss of $140 million on revenue of $221 million.

Quarterly revenue gains are forecast to slow over the first half of fiscal 2020, and Slack isn't expected to turn a profit for at least two more years.

5. -- Zion Williamson Goes No. 1 to the Pelicans

The New Orleans Pelicans selected Duke's Zion Williamson with the No. 1 pick in the NBA Draft, going with the third freshman to be voted player of the year by the Associated Press.

Williamson averaged 22.6 points and 8.9 rebounds while shooting 68% from the field for Duke last season.

Murray State's Ja Morant went to the Memphis Grizzlies with the No. 2 pick and Williamson's teammate at Duke, R.J. Barrett, was selected third by the New York Knicks.

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