Pergamon Tetrahedron Letters 40 (1999) 985-988 TETRAHEDRON LETTERS Synthesis of polycyclic structures by Diels-Alder reaction using inner-outer-ring 1,3-bis[trimethylsilyloxy]dienes Jos~ Pdrez Sestelo, *a M a del Mar Real, a Antonio Mourifio, b and Luis A. Sarandeses *a aDepartamento de Quimica Fundamental e hulustrial, Universidade da Coruha. E-15071 A Coruha, Spain. bDepartamdnto de Qu{mica Orgdmica. Universidade de Santiago de Compostela, E-15706 Santiago de Cornpostela. Spain. Received 23 September 1998; accepted 17 November 1998 Abstract. In this paper we describe regioselective one-pot preparations of inner-outer-ring 1,3-bis[trimethylsilyloxy]dienes and their Diels-Alder reactions with electron-deficient dienophiles. The dienes were prepared in quantitative yield, and the Diels-Alder reactions proceeded smoothly, regioselectively and with good yields, allowing efficient construction of highly functionalized polycyclic skeletons such as naphthofurans, benzofurans and various carbocycles present in natural and non-natural products. © 1999ElsevierScienceLtd. All rights reserved. Keywordz'. Dials-Aider reactions;Dienes;Polycyclic aromaticcompounds; Benzofurans. The Diels-Alder reaction is one of the most powerful C-C bond-forming reactions in natural product synthesis.[1] Over the years, intensive research has led to the preparation of a wide variety of dienes to which it can be applied.[2] In particular, cyclic dienes in which one of the double bonds is endocyclic (inner-outer-ring dienes) are highly valuable for the construction of polycyclic structures.[3,4] Dioxygenated 1,3-butadienes are also of great importance due to the abundance of natural polyoxygenated compounds, to the increased reactivity with dienophiles caused by the synergism between the two oxygen substituents, and to the ease with which the adducts may be selectively converted to enones and aromatic compounds;[5-8] the most important member of this group is undoubtedly the trans-1- methoxy-3-trimethylsilyloxy-1,3-butadiene (1, Danishefsky's diene, Scheme 1). [9-11 ] Scheme 1 TMSO..~/ ;. O ~ OMe OMe 1, Danishefsky's diene ~ OTMS :, O 2, Inner-outer-ring 1,3-bis[trimethylsilyloxy]dienes 0040-4039/99/$ - see front matter © 1999 Elsevier Science Ltd. All rights reserved. PH." S0040-4039(98)02463 -0