Employing a strategy for the construction of fused furans based on an intramolecular [3+2] dipolar cycloaddition reaction of nitrile oxide, the BCD ring system 3 found in the tanshinone family as a common structural unit has been synthesized.

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A fused furan assembling strategy based on an intramolecular [3+2] dipolar cycloaddition reaction of nitrile oxide has been applied to a total synthesis of perfumy furanomonoterpene (+)-menthofuran (1). The key cycloaddition substrates (9) and (1 2) are easily prepared via straightforward routes starting from (+)-citronella1 and these are treated with sodium hypochlorite and pchlorophenyl isocyanate, respectively. The cycloaddition reactions generate 10 : 1 mixture of diastereoisomeric isoxazolines (2a) and (2b) in good to excellent yields. The isoxazolines (2a,b) thus obtained are converted to (+)-menthofuran (1) by sequential reductive hydrolysis and alkaline hydrolysis (or vice versa) followed by acid treatment of the resulting P,y-dihydroxy ketone (14). Menthofuran (I), one of the most well-known members of furanoterpenes, was first obtained by Charabot in 1904 from peppermint oil,' Mentha piperita vulgaris S. Subsequently, Wienhaus2 deduced the structure by a series of chemical experiments and the confirmation of it was made by a combination of the synthesis from pulegone and some chemical techniques by Treibs.3 Menthofuran has sewed not only as an important perfumery, but also as a synthetic intermediate for the other

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Regioselective Intramolecular Photocycloaddition of 1-Cyano-2-(2oxa-4-alkenyl)naphthalenes in the Presence of Eu(III) Salt.-Irradiation of the methylated title compounds (I) or (IV) usually gives a mixture of the cycloadduct at the 1,2-position and the cycloadduct (III) at the 3,4-position. The presence of Eu(hfc)3 affords the (2 + 2) photocycloadducts (II) and (V) regioselectively. However, educt (VI) gives almost no (2 + 2) cycloadduct even in the presence of catalysts. -(MIZUNO, K.; KONISHI, S.; TAKATA, T.; INOUE, H.; Tetrahedron Lett. 37 (1996) 43, 7775-7778; Dep. Appl. Chem., Coll. Eng., Osaka Prefect. Univ., Sakai, Osaka 593, Japan; EN)