George Rosenkranz, a chemist who, with two colleagues, altered human reproductive history in a Mexico City lab in 1951 by synthesizing the key ingredient in what became the oral contraceptive known as “the pill,” died on Sunday at his home in Atherton, Calif. He was 102.

His grandson Adrian Rosenkranz confirmed the death.

Besides a seminal contribution to birth-control science, Dr. Rosenkranz’s team achieved the first practical synthesis of cortisone, the drug used to treat rheumatoid arthritis and reduce painful inflammations in muscles and joints. He was also a world-class contract bridge champion whose wife was kidnapped during a tournament in Washington in 1984 and ransomed for $1 million.

A Hungarian Jew and Swiss-trained chemical engineer who fled fascism as World War II engulfed Europe, Dr. Rosenkranz took refuge in Cuba and after the war became the research director of Syntex, a pharmaceutical lab in Mexico. There, in a scientific backwater, he assembled a small group of chemists who laid the groundwork for revolutionary advances in steroid hormone drugs.

Scientists had long known that high levels of estrogen and progesterone effectively inhibited ovulation. But synthesizing those hormones from animal or plant extracts had been too expensive and relatively ineffective for use in commercial oral contraceptives. In the early 1950s, a race was on among pharmaceutical competitors to crack the chemical code for an ovulation restraint.