Alkylidene-8-Lactones

Schemes 6-26 A proposed reaction pathway for Rh(l)-catalyzed cyclization of a,co-alkynoic acids to alkylidene lactones...

As shown in Eq. 9.48, optically active alkylidene lactones having an iodoalkyl substituent were prepared from the corresponding optically active epoxy alcohol by means of the Sharpless epoxidation. These represent precursors of optically active functionalized cyclopentanes and cyclohexanes, respectively, as shown in the equation [92]. 

Alkylidene lactones. In the presence of this catalyst, alkynoic acids (2) can cyclize to exocyclic enol lactones (3) with marked preference for the Z-isomer. The reaction in CH,C12 proceeds at room temperature. Cyclization to five-mem-... 

Gold intramolecular processes are also possible. Using AuCl and K2C03 as catalysts, Harkat et al. achieved y- and 8-alkylidene lactonizations from co-acetylenic acids by efficient and stereoselective reactions [91]. 

Even six or seven-membered ring lactones were reported by AuCI catalyzed reactions. Pale et al. prepared y- and 6-alkylidene lactones by intramolecular cycliza-tions of co-acetylenic acids. Once again, the process was stereospecific and only Z products were obtained in the case of substituted alkynes [91]. 

The total synthesis of ( )-ancistrofuran has relied on the ene reaction of N-phenyltriazolinedione (PTAD, 564) with the alkylidene lactone (563) (81JOC1198,80JOC4287), Upon completion of this room temperature reaction an attempt was made to acetylate the free NH group in (565) (2 1 mixture of diastereoisomers). The cyclized ethers (566) and (567) were, however, obtained instead. The triazolinedione thus functions as a very good... 

Bp3-Et20 led to a cyclic iron-oxacarbenium salt. Demetalation led to the a-alkylidene lactones. 

An efficient dual photooxidation of compounds comprised of both oxazole and selenide units was demonstrated <86RTC345>. In a single step, the dye-sensitized reaction yields a,fj-unsaturated triamides (66), which may be further transformed into a-alkylidene lactones (67) on heating in the presence of catalytic acid (Scheme 19). 

Eine Reihe von Lactonen wird ausgehend von leicht zuganglichen Lactonen durch gezielte Transformationen hergestellt. So erhalt man z.B. 2-Alkyliden-lactone durch Aldol-Kondensation von Aldehyden mit a-unsubstituierten Lactonen354,355 (s.a.S. 739) [vgl. a. Bd. VI/2, S. 705 (1963)] z.B. ... 

Co(I) or Co(I), Co(III) couples/ Rhodium phosphine complexes cyclize a,a>-alkynoic acids to alkylidene lactone. The suggested mechanism (Scheme 32) is supported by the isolation of two iridium trialkylphosphine complexes (47) and (48), which serve as models for the proposed intermediates A and C and whose crystal structure has been determined. ... 

The masked acrylate anion (70) can be condensed with epoxides leading to a-alkylidene-lactones (71) after a retro-Diels-Alder reaction the generality of this method remains to be seen. Compounds (71) can also be obtained in generally moderate overall yields from enolates of y-trimethylsiloxy-nitriles by... 

Figure 4.1 General structures of a-alkylidene lactones and lactams.

McCurry and Donovan have employed the ylid adduct for the synthesis of alkylidene lactone 88 in high yields (60-78%). The latter are precursors to 3-alkylfurans 89. Use of the ylid 84 has been reported in the synthesis of lysergic acid and as a catalyst for the preparation of phosphine sulfides. Zweifel and coworkers have studied the triphenylphosphine and... 

Alkylidene lactones, MA in synthesis, 231 Alkylmagnesium bromide dialkyl fumarate adducts, 234 dialkyl maleate adducts, 234 Alkylmaleic anhydride, synthesis from alkenylsuccinic anhydride, 175 Alkyl malonates... 

A full report has appeared on the preparation of ( )-a-alkylidene lactones (116) in very high yields from enolates (115). Such a transformation can also be carried out in one-pot directly from butyrolactone, although yields are somewhat lower. One useful aspect is that (Z)-isomers of (116) are formed predominantly if the reaction is run in the presence of a metal halide such as Cul or ZnQi. In a very preliminary communication, it has been shown that virtually pure )- or (Z)-a-ethylidene butyrolactone can be obtained from... 

A stereoselective route to a, -unsaturated esters involves a condensation of the enolate of methyl a-phenylselenyl acetate with carbonyls followed by separation of the resulting diastereoisomeric mixture of -hydroxyselenides and anti-elimination using thionyl chloride or phosphorus oxychloride in the presence of triethylamine. The same method can be used to prepare isomerically pure a-alkylidene-lactones. The a-selenylacetate enolate adds [1,2] to cyclohexenone at —78 °C in THF but this preference may be reversed almost completely by the addition of hexamethylphosphoramide or by warming the reaction mixture to room temperature. 

Chan DM-T, Marder TB, Milstein D, Taylor NJ (1987) Transition-metal-catalyzed cyclization of alkynoic acids to alkylidene lactones. J Am Chem Soc 109 6385-6388... 

Marder TB, Chan DM-T, Fultz WC, Calabrese JC, Milstein D (1987) Mechanistic studies of the rhodium-catalyzed cyclization of am-alkynoic acids to alkylidene lactones. Cristal structure of two iridium model catalytic intermediates. J Chem Soc Chem Commun 1885-1887... 

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