Cyclisation of 3-methylcyclohex-2-enones and the derived epoxides containing alkene, alkyne, and aryl side-chains yields bicyclo [4.4.0]decane derivatives when the alkene or alkyne is electronically biased towards six-membered ring formation and when the alkene is electronically unbiased.
M 13 9PL 2-Substituted 3-methylcyclohex-2-enones and the derived epoxides have been cyclised to a variety of hydrindanone derivatives. When the 2-substituents are pent-3-ynyl or 4-chloropent-3-enyl the cyclisations take a predictable course ; however, with 4-methylpent-3-enyl in the enone, the initial cyclisation product undergoes hydride and methyl migration. In the related epoxide an unexpected 'ene ' reaction occurs.Cation-induced cyclisation of appropriate electronically unbiased alkenes predominantly favours six-membered ring formation (6-endo-Trig) rather than five-membered ring formation (5-exo-Trig). When substitution on the alkene is electronically biased in favour of the latter such cyclisation does occur but is frequently followed by secondary processes such as hydride or alkyl migrations.2 In order to test the feasibility of 5-membered ring formation using cyclohexenone derivatives as initiators, we examined the cyclisation of compounds (1)-( 6). Reaction of (4) with SnCl4-CH2CI2 at -20 "C gave a product (9479, the analytical and spectroscopic properties of which [ v, , .
Reaction of the epoxy-olefin (1) with Lewis ring formation (BExo-Trig) by electronically biasing the acids gave the bicyclo[3.3.l]nonane derivative (2), double bond. Cyclisation of (1) with SnC1,-CH,Cl, a t possibly by an 'ene' reaction.-20 "C gave (3) (94%), [Vmax (CHCI,) 3490 and 1715 cm-l;T (CDCl,) 9-0 (3H, s). 8-3 (3H s), 5.26 (lH, s), and 5-13 (lH,
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