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Le traitement du 2,3-dibromo-1-benzenesulfonyl-1-propene avec des composes β-dicarbonyles en presence de methoxyde de sodium conduit avec un haut rendement au furane bicyclique 2,4-disubstitue et au furane bicyclique 2,3-fusionne. La formation du cycle furane implique une sequence d'addition-elimination, une deacetylation et des reactions de deplacement de type SN2

2,3-Dihalo-1-(phenylsulfonyl)-1-propenes, obtained by the addition of bromine or iodine onto (phenylsulfonyl)propadiene, were found to exhibit interesting reactivity as both mono- and dielectrophiles, with the mode of reactivity depending upon the nature of the nucleophile as well as the reaction conditions. Thus, amines or thiophenols smoothly effected substitution at the allylic site, while sodium methoxide reacted at the vinylic position through an addition-elimination process

Recent progress in the development of new strategies and tactics for natural products synthesis is described. An emphasis is placed on the development of new sequences of radical reactions. A new approach to the crinipellin family of tetraquinanes and a recently completed formal total synthesis of camptothecin are highlighted. We recently compiled a review to bring together recent advances in "Radical Reactions in Natural Products Synthesis."' This paper will summarize some of our recent progress in developing new strategies for the use of radical reactions in the synthess of natural products. Often, the implementation of these new strategies will require the development of new reactions. Most synthetic applications of radical methods conduct only one key reaction in between generation of a radical and its removal.2 Starting from our earliest work in this field, one of our major themes has been the sequencing of radical reactions.3 Radical reactions are naturally suited to sequencing because the product of every radical reaction is a radical. We defiie a tandem radical reaction as a sequence of radical reactions which has inore than one step between radical generation and radical removal. Chemoselectivity is a big issue in tandem sequences, and a variety of powerful strategies have emerged to solve selectivity problems.*a,4 One of the simplest, yet most powerful, strategies is to plan only rapid intramolecular radical reactions between radical generation and removal. In this way, it is often as easy to form two or three bonds as it is to form one. This tandem cyclization strategy has been an early and continuing theme in our work.3 Figure 1 uses a new radical notation4 to summarize tandem radical strategies to two large, important classes of triquinane sesquiterpenes: linear and angular.5 Though the two ring systems are quite different, the strategies are closely related. Each case calls for a central cyclopentene ring bearing two side chains: one with a radical donor and one with a radical acceptor. The tandem cyclization then occurs through the middle of the cyclopentene ring. The only difference between the two strategies is where the two side chains are located on the central ring.