TETRAHEDRON LETTERS Tetrahedron Letters 42 (2001) 4373–4376 Pergamon Assembling monocyclic, spirocyclic and fused carbocycles by ring-closing metathesis on an arene–chromium template Bikash C. Maity, Vishwanath M. Swamy and Amitabha Sarkar* Divisions of Organic Chemistry (Synthesis), National Chemical Laboratory, Pune 411008, India Received 26 February 2001; accepted 27 April 2001 Abstract—A variety of diene precursors assembled stereoselectively on an arene–chromium template underwent facile ring-closing metathesis by ruthenium catalysis at ambient temperature to afford cyclic compounds of varying degrees of complexity in high yields. © 2001 Elsevier Science Ltd. All rights reserved. Ring-closing metathesis (RCM) has become a powerful tool for the ready construction of cyclic structures over the past few years 1 with the availability of structurally defined, mononuclear metal catalysts developed by Schrock 2 [2,6-i Pr 2 C 6 H 3 NMo{OC(CF 3 ) 2 Me} 2 CHCMe 2 - Ph] and Grubbs 3 [Cl 2 {(c -C 6 H 11 ) 3 P} 2 RuCHPh]. A sig- nificant, practical advantage of Grubbs’ ruthenium cat- alyst is derived from its relative stability to air and moisture, in addition to its tolerance of a wide variety of functional groups. Almost an infinite variety of structures are amenable to RCM. Since an alkene is the product of metathesis, chiral cyclic products are usually synthesized from pre- assembled chiral dienes, 4 while only a few examples exist in the literature pertaining to chirality originating from RCM. 5 Arene–chromium complexes provide a ready access to diastereomerically pure compounds of diverse struc- tural types. 6 The present report describes the use of RCM to synthesize a variety of diastereomerically pure carbocyclic as well as heterocyclic products at ambient temperature, from differently substituted diene precur- sors assembled on arene–tricarbonylchromium tem- plates in high yield. The products are monocyclic, spirocyclic or fused polycyclic compounds depending on the design of the precursors, and feature one to three stereogenic centers. This study complements recent efforts to create stereochemically defined molecu- lar scaffolds 7 and the use of organometallic precursors 8 for this purpose. The substrates were independently synthesized by appropriate procedures. Complex 1 was synthesized in three steps from an o -methylacetophenone–Cr(CO) 3 complex. Claisen–Schmidt condensation with p -tolu- aldehyde was followed by addition of MeLi in ether. The 1,2-adduct was obtained as the major product 9 and as a single diastereomer, which was converted to the allyl ether 1a by a standard procedure. The stereochem- istry of the new stereogenic center was assigned based on an exo -selective attack on the sterically preferred anti conformer. 10 The optically pure substrate 2a was derived from the optically pure o -anisaldehyde–Cr(CO) 3 complex, 11 the product resulting from an exo addition to the more stable anti conformer. 12 The stereochemistry of sub- strate 3a was assigned on similar considerations. RCM with Grubbs’ ruthenium catalyst at ambient tempera- ture in dichloromethane yielded 13 the corresponding heterocycles in respectable isolated yields (Table 1). Spirocycles 4b and 5b were similarly obtained from RCM of relevant substrates 4a and 5a, respectively, which in turn were prepared by well-precedented 14 exo - selective allyl Grignard addition to 1-tetralone– and 1-indanone–Cr(CO) 3 complexes. Based on an earlier report 15 from this laboratory, the synthesis of substrates 6a and 7a was accomplished according to the reaction sequence depicted in Scheme 1. * Corresponding author. 0040-4039/01/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved. PII:S0040-4039(01)00713-4