. Can. J. Chem. 58,755 (1980) A total synthesis of (+)-stemarin, a diterpenoid with a unique C/D ring system, is described. The synthesis features photoaddition of allene to an a,P-unsaturated ketone and two skeletal rearrangements. Application of the synthetic strategy described herein to a synthesis of stemodinol and aphidicolin is anticipated. RONALD B. KELLY. MARY LOU HARLEY et SASDRA J. ALWARD. Can. J. Chem. 58,755 (1980). On decrit une synthese totale de la (+) sttmarine, un diterpene ayant un systeme cyclique C/D particulier. La synthese est caracterisee par I'addition photochimique d'un allene sur une cetone a ,P non saturee et par deux transpositions moleculaires. On envisage d'appliquer la strategie decrite a la synthese du stemodinol et de l'aphidicoline.[Traduit par le journal]Because of their unique structures, the diterpenoids stemarin (I) (I), stemodinol (2), and their relatives (2, 3) are attractive candidates for total synthesis. While contemplating syntheses of these diterpenoids, it occurred to us that they might be obtained via rearrangement of epimeric intermediates such as 3a and 3b where migration of bond a would lead to the stemarin skeleton and migration of bond b to the stemodinol skeleton. Since bond migration would be controlled by the stereoalignment of the migrating bond relative to the leaving group (OTs), 3a should rearrange to the stemarin skeleton and its epimer (3b) to the stemodinol skeleton. We now wish to describe a total synthesis of stemarin (1) by application of this strategy .'The tosylate 3a was prepared from the totally synthetic (5) racemic ketone 4 along lines previously employed in these laboratories (6) involving photoaddition of allene to 4 and subsequent skeletal rearrangement. Thus, stereo-and regiospecific photoaddition of allene to 4 afforded, in 78% yield, the adduct 5 (mp 121°C; ir: 1662 and 900 (olefin) cm-l; nmr 6: 4.90 (m, 2H, vinylic proton^))^ which, on treatment with methyl iodide in T H F in the 'A synthesis of aphidicolin (4) by a similar strategy can be envisaged; for syntheses of aphidicolin by a different approach, see refs. 4b, c .ZThroughout, their spectra (in Nujol unless specified) and the nmr spectra (in CDC1,) are entirely consistent with assigned structures. Satisfactory elemental analyses were obtained for all crystalline compounds and correct molecular ions were found in the mass spectra of the remaining compounds.presence of LDA at -10°C, gave (74% yield) the ketone 6(mp 124°C; nmr6: 1.16 (d, J = 6.5 Hz, 3H, secondary methyl)). The ketone 6 was converted in the usual manner, in 90% yield, into the ketal7 (mp 131°C; nmr 6 : 3.64 (br s, 4H, ethylene of ketal)).