As shown in Scheme 2, the next phase involved addition of the carbon atoms required for the formation of the C ring. Ketone 7 was treated with magnesium bromide diisopropylamide and underwent an aldol reaction with 4-pentanal (8) to give β-hydroxyketone 9. The hydroxyl group was protected as the asymmetric carbonate ester (10).  Oxidation of the enolate of ketone 10 with (-)-camphorsulfonyl oxaziridine (11) gave α-hydroxyketone 12. Reduction of the ketone group with 20 equivalents of sodium bis(2-methoxyethoxy)aluminumhydride (Red-Al) gave triol 13, which was immediately converted to carbonate 14 by treatment with phosgene. Swern oxidation of alcohol 14 gave ketone 15. The next step set the final carbon-carbon bond between the B and C rings. This was achieved through a Chan rearrangement of 15 using lithium tetramethylpiperidide to give α-hydroxylactone 16 in 90% yield. The hydroxyl group was reductively removed using samarium(II) iodide to give an enol, and chromatography of this enol on silica gel gave the separable diastereomers cis 17c (77%) and trans 17t (15%), which could be recycled to 17c through treatment with potassium tert-butoxide. Treatment of pure 17c with lithium tetramethylpiperidide and (±)-camphorsulfonyl oxaziridine gave separable α-hydroxyketones 18c (88%) and 18t (8%) in addition to some recovered starting material (3%). Reduction of pure ketone 18c using Red-Al followed by basic work-up resulted in epimerization to give the required trans-fused diol 19 in 88% yield.