In the early 1960s Dassault was seeking a US partner to license build the Falcon 20 business jet for the US market. Grumman, Lockheed, North American, and McDonnell were out as they had their own business jet designs in development (Gulfstream, Jetstar, Sabreliner, and McDonnell 119/220, respectively). Douglas was already working with Piaggio on the PD-808 "Vespa Jet", Beechcraft had formed an alliance with Hawker Siddeley on the HS.125, and Convair was mired in problems with their CV-880/990 jetliners.
That left Boeing. Dassault approached Boeing and the the board of directors after careful examination of Dassault's proposal elected to not invest in the bizjet market, preferring to continue to keep its capital in its growing commercial airframe business.
Source: Flightpath, Volume 2/Winter 2003. "Dassault Falcon: Mystere Magic" by David Donald (Variant File), p84.