New Routes by the Merck Group

Transformation of (43) into (44), followed by lactonization, a-formylation [to (45)], ozonolysis, and acetylation, then produced the dihydro-a-pyrone 

AcaO vi, Ha-Pd/C vii, Collins oxidation viii, (MeOaXOP CH-COCsHu ix, Zn(BHi)2 x, hydrolysis followed by chromatography xi, NaOH xiii, HOAc-HjO. 

Reagents i, Oj ii, AcaO-NaOAc iii, HO(CH2)aOH-H+ iv, NaOH v, LKOBuOsAlH on acylimidazole vi, RuOa-NaI04 vii, NaOMe viii, CF3CO3H, Na,HP04 ix, C5HiiCOCH2PO(OMe)a-NaH 

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New Routes by the Merck Group.—The Merck group have published two new routes to PGEi. The first of these involves the initial preparation of a key intermediate (43) in their earlier route, and starts from the optically resolved Diels-Alder adduct (39) from tranj-piperylene and maleic anhydride (Scheme 8). Homologation to (40) followed by iodolactonization, esterification, and reduction furnished (41), which was saponified, dehydrated, and re-esterified to (42). Cyclization, followed by alkylation, hydrolysis, and decarboxylation, then produced an acid, which was esterified to give (43). 

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