3-Methylcyclohex-2-enone derivatives as initiators of cyclisation. Part 3. Cyclisation to form five-membered rings

Abstract

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, , .

The Prins and Carbonyl Ene Reactions

“…Similar cyclization of (92) gives (96) in 83% yield in 32% enantiomeric excess. The ene reactions of (85), (90), (91) Type I ene reactions with less nucleophilic 1,2-disubstituted double bonds have been more problematic. 75 Ene reaction has been achieved using 1 equiv.…”

Stereoselective Synthesis of Bicyclic Tertiary Alcohols with Quaternary Stereocenters via Intramolecular Crossed Benzoin Reactions Catalyzed by N-Heterocyclic Carbenes

“…The target compounds 1 are tertiary alcohols having quaternary stereocenters at the two adjacent bridgehead positions. Interestingly, a series of homologues 1 , except for racemic 1d , are new compounds, which may suggest that they are difficult to prepare by other synthetic methods. Further conversions of 1 into other new compounds can also be expected.…”