[2][4] At Syntex corporation in Mexico City, Rosenkranz assembled a research group of organic chemists that included future leaders from around the world, such as Carl Djerassi, Luis E. Miramontes and Alejandro Zaffaroni.

Under Rosenkranz's leadership, Syntex became "a powerful international force in the development of steroidal pharmaceuticals",[12] and "a pioneer of biotechnology" in the San Francisco Bay Area.

Unable to go to Ecuador, Rosenkranz accepted the Cuban president Fulgencio Batista's offer allowing refugees to stay in the country and work.

He didn't have much help: his initial staff included nine lab assistants and only one other chemist,[19] and Mexico lacked a PhD program in chemistry.

[20] Attracting young chemists such as Carl Djerassi, Luis E. Miramontes and Alejandro Zaffaroni was critical to Syntex's first big success.

[5][6] Miramontes, George Rosenkranz and Djerassi synthesis of norethindrone, later proven to be an effective pregnancy inhibitor, led to an infusion of capital in Syntex and Mexican steroid pharma industry.

[22] The Mayo clinic had reported that the steroid hormone cortisone was an effective anti-inflammatory, capable of relieving painful rheumatoid arthritis symptoms.

In 1951, Rosenkranz, Djerassi, and their fellow researchers submitted a paper on the synthesis of cortisone, edging out reports from Harvard and Merck by a matter of weeks.

[4][25][27] Syntex initially reached an agreement with the American company Parke-Davis to market norethisterone as Norlutin for the treatment of gynecological disorders, which was approved by the FDA in 1957.

[20][30][31] In March 1964, the FDA also approved Parke-Davis's version of the German company Schering's oral contraceptive Anovlar with the brand name Norlestrin (norethisterone acetate 2.5 mg + ethinylestradiol 50 μg).

He has said, "To have people work productively, you have to build an intellectually challenging environment, allow creative freedom, and insure peer recognition and respect for the individual.

He won 12 NABC-level events at thrice-annual North American Bridge Championships meets, including all four major teams-of-four titles: the Grand Nationals, Reisinger, Spingold and Vanderbilt.

[4] In July 1984, Rosenkranz' wife Edith was kidnapped at the summer North American Bridge Championships in Washington, D.C., by Glenn I. Wright and Dennis Moss, and ransomed for one million dollars.

The second, and first with co-author credit to Phillip Alder, Godfrey's Bridge Challenge "brings the Romex system to life through lively anecdotes instruction and quizzes".