Journal of Molecular Catalysis A: Chemical 164 (2000) 165–171 Rhodium(II) catalysed decomposition of 3-diazo-4-hydroxycoumarin An easy access to furocoumarin ring system Sergio Cenini a , Giancarlo Cravotto b , Giovanni B. Giovenzana c , Andrea Penoni a , Stefano Tollari d,∗ , Giovanni Palmisano d,∗ a Dip. di Chimica Inorganica Metallorganica e Analitica and CNR Center, Via Venezian 21, 20133 Milano, Italy b Dip. di Scienza e Tecnologia del Farmaco, Via Giuria 9, 10125 Torino, Italy c Dip. di Scienze Chimiche Alimentari Farmaceutiche e Farmacologiche, Viale Ferrucci 33, 28100 Novara, Italy d Dip. di Scienze Chimiche, Fisiche e Matematiche, Via Lucini 3, 22100 Como, Italy Received 3 April 2000; received in revised form 18 July 2000; accepted 18 July 2000 Abstract Several furo[3,2-c]coumarins are produced efficiently and regioselectively by a formal [3+2] cycloaddition of 3-diazo-4- hydroxycoumarin and oxygenated alkenes, presumably via the intermediacy of rhodium carbenoid. © 2000 Elsevier Science B.V. All rights reserved. Keywords: Rhodium(II); Furocoumarin; -Diazocarbonyl 1. Introduction Metal induced diazo compound decomposition, re- ported since 1906 [1], is a convenient method to gen- erate transient carbenoid species; these react with a large variety of functional groups, giving either addi- tion to multiple bonds or insertion into single bonds, making this protocol an useful tool in synthetic or- ganic chemistry [2–9]. -Diazocarbonyl compounds extend the prepara- tive purposes of this reaction; the functional group  to the electrophilic carbenoid centre allows further evolution of the initial addition/insertion products ∗ Corresponding author. Tel.: +39-2-266-80675; fax: +39-2-2362748. E-mail address: tollari@mail.csmtbo.mi.cnr.it (S. Tollari). ultimately giving interesting ring systems [10–13]; the larger (thermal) stability of -diazocarbonyls with respect to unfunctionalized ones is another advantage. A great number of catalytic systems based on tran- sition metal derivatives have been investigated for the diazo-decomposition; between them rhodium(II), and particularly Rh 2 (OAc) 4 , is the most effective to gen- erate reactive metal-carbenoid species. In a precedent work [14], we explored the chemistry of the carbenoid system derived from Rh(II)-decomposition of 3-diazo-4-hydroxycoumarin 1 in cyclic ethers, obtaining coumarin-fused crown ethers. We report here a facile and efficient construc- tion method of fused furocoumarins by the use of a Rh(II)-induced [3+2] cycloaddition of 1 and oxy- genated alkenes 3 (Eq. (1)). Since many naturally derived coumarins embody furo[3,2-c]coumarin ring 1381-1169/00/$ – see front matter © 2000 Elsevier Science B.V. All rights reserved. PII:S1381-1169(00)00372-1