Tandem rearrangements of a cyclic bis-allene Hussein H. Mustafa a , Mark S. Baird a, * , Juma’a R. Al Dulayymi a , Viacheslav V. Tverezovskiy b a School of Chemistry, Bangor University, Bangor, Wales LL57 2UW, UK b BioComposites Centre, Bangor University, Bangor, Wales LL57 2UW, UK article info Article history: Received 20 September 2013 Received in revised form 5 December 2013 Accepted 20 December 2013 Available online 8 January 2014 This paper is dedicated to the late Ivan Bo- lesov, scholar, supervisor and friend Keywords: Cyclopropylidene Allene Ene-reaction Sigmatropic shift abstract Reaction of the bis-dibromocarbene adduct of cyclonona-1,4,7-triene with methyllithium leads to a mixture of meso and racemic cycloundeca-1,2,5,6,9-pentaenes; the former rearranges at ambient temperature through a set of pericyclic reactions. Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction The reaction of 1,1-dibromocyclopropanes with methyllithium provides a very efficient approach to allenes (Scheme 1). It is thought to occur by lithiumebromine exchange followed by for- mation of a cyclopropylidene (3) or a related carbenoid. 1 In many cases, the reaction proceeds in a few minutes even at 100  C, though at lower temperatures, the lithiobromocyclopropane (2) may be trapped with electrophiles in inter- or intra-molecular processes; for example, on quenching with methanol, a mono- bromocyclopropane can be obtained. It has been used to produce cyclic mono- and bis-allenes, 2e14 and it is over 50 years since Moore and Ward and Skattebøl re- ported the first such products. 8e10 However, where the strain generated in producing the allene is high or when there is another favourable carbene reaction available, alternative reactions, such as cyclopropylidene insertion into CeH bonds, 4,7,15e18 addition to double bonds, 19,20 or rearrangement, 21 may occur. In other situa- tions, the intermediate 2 is trapped in intramolecular processes. 22 We have recently reported the generation of two di- astereoisomers, 6 and 7 , of the tris-allene, cyclododeca-1,2,5,6,9,10- hexaene from the tris-dibromocarbene adduct of cyclonona-1,4,7- triene, compound 5, on reaction with methyllithium (Scheme 2). 23 It is also known that the mono-dibromocarbene adduct of the triene, compound 8, reacts with methyllithium to give the corre- sponding allene, cyclodeca-1,2,5,8-tetraene (9) in 78% yield (Scheme 3). 24 Scheme 1. Scheme 2. * Corresponding author. Tel.: þ44 1248 382374; fax: þ44 1248 370528; e-mail address: chs028@bangor.ac.uk (M.S. Baird). Contents lists available at ScienceDirect Tetrahedron journal homepage: www.elsevier.com/locate/tet 0040-4020/$ e see front matter Ó 2014 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.tet.2013.12.058 Tetrahedron 70 (2014) 1502e1507