A-Methylenebutyrolactones, synthesis

Lactones General Synthesis Synthesis of P-Lactones Synthesis of Butyrolactones Synthesis of Butenolides Synthesis of Phthalides Synthesis of Tetronic Acids Synthesis of a-Methylenebutyrolactones Synthesis of Valerolactones... 

Another approach is the Michael addition to ethyl (3-nitroacrylate, as shown in Eq. 7.123, which has been used in the synthesis of a-methylenebutyrolactone, a moiety characteristic of many sesquiterpenes. ... 

The generation of exocyclic double braids by rDA cycloreversion is usefrd for the synthesis of unsaturated lactones, which are an important part of many natural products. The a-methylenebutyrolactone tuli-... 

Acidic Fragmentation in the Course of a Clever Synthesis of o-Methylenebutyrolactones... 

The remaining bond rupture would afford a relatively more stable carb-anion on the butyrolactone ring of VII, a fundamentally acidic position widely employed in organic synthesis. The freed pair of electrons would then proceed to force the extrusion of an oxalic acid residue yielding the desired a-methylenebutyrolactone. The concerted addition-elimination process from VI to II is also a feasible alternative. 

An alternative synthesis of a-methyiene ketones and esters is provided by enolate alkylation using benzyl bromomethyl sulfide followed by oxidative elimination (Scheme 10). The addition of sodium thiophenoxide to a-methylenebutyrolactones has been recommended for protection of the sensitive double bond, which can be regenerated by oxidative elimination. ... 

Loeffler, A., Pratt, R. D., Pucknat, J., Gelbart, G., Dreiding, A. S. Preparation of a-methylenebutyrolactones by the Reformatskii reaction synthesis of protolichesterinic acid. Chimia 1969, 23, 413-416. 

The rich and varied chemistry of metal-carbene complexes outlined in this chapter should eventually lead to the wide use of metal-carbene complexes in organic synthesis. To date, carbene complexes have not been used extensively as their chemistry was not widely understood and the reagents are moderately expensive. However, the applications of metal-carbene complexes in peptide synthesis, in the synthesis of an indole alkaloid, and in the synthesis of a-methylenebutyrolactone have been reported. These applications indicate some of the ways in which metal-carbene complexes may prove useful in synthesis. 

The intermediate a-sulfenyl carbonyl compounds may be alkylated prior to oxidative elimination. Phe-nylsulfenylation of the m-fused butyrolactone (61), followed by methylation and oxidative elintinadon, gave the a-methylenebutyrolactone (62) because endocyclic elimination is sterically inhibited (Scheme 6). For the tran -fused butyrolactone (63), the alkylation was carried out first to ensure exocyclic elimination (Scheme 7). The intermediate a-sulfinylcarbonyl compounds may also be modified before elimination, the alkylation of keto sulfoxides (64) providing a useful synthesis of a, -unsaturated y-keto esters (65 Scheme In some cases the use of an excess of strong base provides a dimetallated... 

A potentially more simple procedure is the Reformatsky condensation of the bromoester (47) with ketones a-methylenebutyrolactones are produced, in one step, in fair to good yield. An efficient three-step synthesis consisting of ketone enamine formation, Michael addition to ethyl / -nitro-acrylate, and borohydride reduction has been reported the last process affords a mixture of the cw-butyrolactone and the /ra j-hydroxyester as shown in Scheme 14. 

Synthesis of a-Methylenebutyrolactones.—The readily prepared allyl silanes (208) are converted into the a-methylenebutyrolactones (210) in good yield via the allylic alcohols (209) (Scheme 111). ... 

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