Optimization of Steroid Photochemistry and Its Application in the Synthesis of 5,6-Dihydro-Ophiopogonol A.

The photoreactivity of steroids represented a hot topic in the middle of the last century and in this project, we "rediscover" it through the exploration of the photochemical behavior of Δ-3-keto-steroids. In terms of number of products obtained, the photochemistry of Δ-3-keto-steroids is less complicated than that of Δ-3-keto- and Δ-3-keto-steroids, furnishing an efficient and tunable method to remodel the classic steroid 6/6/6/5 ring system. In this scenario, this approach can represent a simple strategy to interconvert a class of easily available steroids to another difficult-to-access from natural sources. As a proof of concept, the synthesis 5,6-dihydro-ophiopogonol A (11), a very close analog of natural ophiopogonol A (7), was accomplished in just four steps starting from easily available diosgenin (8).