Synthesis enolates from

The stereoselective introduction of both benzyl groups simultaneously in one step seemed to be particularly attractive for a short synthesis of a- hy-droxylated lactone lignans from malic acid (99). Such a simultaneous double alkylation requires the formation of a chiral l,3-diene-l,4-diolate, which was not known. On the other hand, achiral 1,3-diene-1,4-diolates (di-enolates) have been previously prepared by Garrett et al. [58] and subsequently employed for the synthesis of racemic lignans by Snieckus [59] and Pohmakotr [60]. With knowledge of the synthesis and reactivity of di-enolates, we planned to prepare chiral di-enolates from dioxolanones and to alkylate these di-enolates in a stereocontrolled manner (Scheme 22). For the development of the described double deprotonation/alkylation strategy, tert-hutyl... 

An attempted synthesis of dithioesters 220 by stepwise treatment of enolates from cyclopropanes 97 with carbon disulfide and methyl iodide lead to an unexpected new product without a cyclopropane ring. By spectroscopic means and study of the reactions dihydrothiophene structure 222 has been established 98). 

Whitesell, J.K. Whitesell, M.A. Synthesis, (1983) 517 "Reactive Enolates from Enol Silyl Ethers"... 

B. Synthesis of Enolates from Enol Ethers and Esters. 542... 

The synthesis, starting from a bifunctional initiator followed by quenching the double-headed living ends, gives homotelechelic polymers (method B). Carboxylate-capped telechelic poly(isobutyl vinyl ether) has been obtained in this way [82], where the adduct of a bifunctional vinyl ether with trifluoroacetic acid is the initiator, and the quencher is the malonate anion. For method C, a bifunctional trimethylsilyl enol ether, CH2=C[OSi(CH3)3]C6H4OCH2CH20C6H4[(CH3)3SiO]C=CH2, is a useful terminator (chain coupler) for vinyl ethers [142,147] and a-methyl-styrene [159] (see also Section VI.B.4). 

The tricyclic ketone (17), a fragrant and volatile key compound of the zizaene (19) synthesis, results from a fragmentation of the tetracyclic mesylate (16). This skeleton has also bron formed by intramolecular photocycloaddition of the easily accessible enol acetate (18). Obviously, the ting strain of (16) is a strong driving force (Scheme 10). 

---