DIBAL-H

Fig. 5. Corey synthesis ofPGE2 and PGF2Q, where DiBAL-H = diisobutylaluminumhydride MCPBA = m — chloroperbenzoic acid py = pyridine ...

Fig. 8. Synthesis of PGE using an organocuprate reagent where DiBAL-H is diisobutylalurninurnhydride and R = (CH2 )g COOCH2 CH3.

Reduction of pehydropyrido[l, 2-u]pyrimidine with DIBAL-H in toluene led to the formation of 1,5-diazacyclodecane in 60% yield (99JCS(CC)1279). 

With the co side chain at C-12 in place, we are now in a position to address the elaboration of the side chain appended to C-8 and the completion of the syntheses. Treatment of lactone 19 with di-isobutylaluminum hydride (Dibal-H) accomplishes partial reduction of the C-6 lactone carbonyl and provides lactol 4. Wittig condensation8 of 4 with nonstabilized phosphorous ylide 5 proceeds smoothly and stereoselectively to give intermediate 20, the bistetra-hydropyranyl ether of ( )-1, in a yield of -80% from 18. The convergent coupling of compounds 4 and 5 is attended by the completely selective formation of the desired cis C5-C6 olefin. 

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