2b 2a 1 Si R R' Si R R' R" Si R R' R" α γ + 1. n-BuLi 2. R"X Si R R' n 3 2 t-BuLi Si R R' Si R R' Si R R' Si R R' MgBr Cl Cl OH R" R" OH 6 5 4 + 7 8 2 RCM TETRAHEDRON LETTERS Tetrahedron Letters 42 (2001) 581–584 Pergamon A new regio- and stereocontrolled access to functionalised silacyclopent-3-enes † Yannick Landais* and Sheetal S. Surange Universite ´ Bordeaux -I, Laboratoire de Chimie Organique et Organome ´tallique, 351, Cours de la Libe ´ration, 33405 Talence Cedex, France Received 18 July 2000; accepted 7 November 2000 Abstract—C-2 functionalised silacyclopent-3-enes were obtained in high yields in only two steps from diallyldiphenylsilane through hydroxy-alkylation of an allyltitanium intermediate followed by ring closure metathesis of the resulting -hydroxysilane. © 2001 Elsevier Science Ltd. All rights reserved. Silacyclopent-3-enes 1 widely used as polymer precursors are attractive synthons that have found little use as building blocks in organic synthesis. 1 These are most commonly accessible by a coupling reaction between dichlorosilanes and dienes in the presence of lithium or magnesium. 1e–f This method, which affords the titled compounds in moderate to good yields, is, however, not general owing to the restricted number of substituents allowed on the ring and at the silicon centre. Moreover, the access to polysubstituted silacyclopent-3-enes through alkylation of 1 is not straightforward. For instance, the preparation of C-2 substituted silacy- clopent-3-enes 2a through metallation of 1 with a strong base (i.e. t -BuLi) followed by alkylation is precluded by the formation of polymeric materials 3 formed by initial nucleophilic attack on the silicon centre (Scheme 1). 2 Increasing the steric hindrance to slow down the attack of RLi on the silicon centre was shown to partially overcome this problem. 2 However, the reaction of the allylic carbanion with a range of electrophiles was found to be poorly regioselective affording inseparable mixtures of /-regioisomers (i.e. 2a and 2b). Therefore, while few methods are available and give access to various types of silacyclopentenes, 1 a general and regioselective method of preparation of synthons such as 2a that could also be extended into homochiral series is still lacking. Scheme 1. Scheme 2. Keywords : silicon and compounds; titanium and compounds; metathesis; hydroxylation. * Corresponding author. Fax: (33) 5 56 84 66 46; e-mail: y.landais@lcoo.u-bordeaux.fr † Dedicated to Dr. Ian Fleming on the occasion of his 65th birthday. 0040-4039/01/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved. PII:S0040-4039(00)02004-9