d 5 ‐Reactions of Doubly Deprotonated γ,δ‐Unsaturated Carbonyl Derivatives with Electrophiles. A Novel Approach to the Synthesis of Tetrahydrofuran and Tetrahydropyran Derivatives

The dienone‐dianion derivatives 1 react with all types of electrophiles tested (alkyl halide, silyl chloride, ester, ketone, aldehyde, epoxide) to give β, γ‐unsaturated carbonyl compounds of type A (see Formulae 2 – 6 , 13 , 14 and Tables 1–5 ). The α‐ and β‐hydroxyalkylation products obtained from 1a – 1d can be converted to tetra‐hydrofuran and tetrahydropyran derivatives 7 and 16 , respectively ( Tables 1 and 2 ), those from the sulfur analogues 1e and 1f to ketene thioacetals 9 and to dienone derivatives 10 and 12. The t ‐butyl and α‐hydroxy‐ketones are cleaved to give nitriles, amides, carboxylic acids and esters ( Formulae 16 ‐ 25 ). The reagents 1 allow to synthesize products with distant functional groups in one step ( cf. 1,8‐diketones 14 and Formulae 26 – 30 ); they correspond to the d 5 ‐synthons 31 – 33 ; in Table 6, they are compared with other d 5 ‐reagents.