Disconnection at b and d

An approach by Chen et.al., (Tet. Lett., 2961 (1993)) relied on the free radical cyclization reaction on a suitably fuctionalized C ring (Figure 1.1). The synthesis of C ring is achieved via., a DA reaction. Knoevenagal reaction placed the required chain for completing the A and B rings. Tin hydride reduction generated a free radical at the site of the nitro group, which underwent a tandem cyclization to complete the A and B rings in that order.

Figure 1.1