A-alkylidene-8-lactones

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). 

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.

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. 

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

In an approach to FR182877, Sorensen and co-workers generated allenoate intermediate 289 from an ce-bromo-ce,/j-unsaturated lactone and effected an intramolecular acylation to afford a-alkylidene-/3-keto-y-lactone 290 as a single stereoisomer (Scheme 19.52) [61]. Evidence for the allenoate intermediate was established by the treatment of a-bromoenoate 291 with tBuLi, which afforded the cydized compound 292 as a single stereoisomer. Treatment of the isomeric bromoenoate of compound 291 also gave 292. Hence this demonstrated a stereoselective but not stereospecific process. 

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... 

Triphenyl phosphite ozonide, 334 Unsaturated lactones a-Alkylidene-7-lactones Chloromethyldiphenylsilane Butenolides... 

A review on ynolates, including the synthesis of p-lactones, has appeared <03S2275>. Morita-Baylis-Hillman-type adducts have been converted into a-alkylidene-p-lactones 65, which on reaction with dimethyltitanocene can be transformed into 3-alkylidene-2-methyleneoxetanes <03OL399>. Lactones 66 have been obtained via the cinchona alkaloid-catalyzed dimerization of monosubstituted ketenes <03OL4745>. The PdCh-promoted synthesis of P-lactones 67 have been achieved via cyclocarbonylation of 2-alkynols <03OL4429>. 

This type of alkynol ether hydrocyanation gives rise to a new stereospecific route to a-alkyli-dene y-lactones. Acidic hydrolysis and cyclization of some of the products obtained, as above, give a-alkylidene-y-lactones in 65-83% yield with the double-bond geometry predetermined via stereoselective hydrocyanation2T... 

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. ... 

B.V. The Stobbe Condensation. When succinic ester derivatives (such as diethyl succinate, 215) are condensed with non-enolizable ketones or aldehydes in the presence of base, the initial condensation product is 216. The alkoxide reacts with the distal ester via acyl substitution to give a lactone intermediate (217). In the original version of this reaction, saponification of 217 gave the a-alkylidene monoester, 218. The reaction is not completely general and is limited to those a, co-diesters for which the Dieckmann condensation is not a... 

Allenes A convenient synthesis of allenes is accomplished by thermolysis of a-alkylidene-P-lactones in DMF. The substrates are avaUable from P-lactones by benzeneselenylation followed by oxidative elimination. 

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. ... 

An interesting and useful synthetie method of y-lactones has been developed by Lu and co-workers based on an intramolecular version of the haloallyla-tion reactions [149]. PdCU or Pd(OAc)2-LiCl-catalyzed reaction of the 3 -(chloro-methyl)-2 -alkenyl 2-alkynoates 377 affords the a-alkylidene-jS-vinyl-y-butyro-lactones 379. The first step is chloropalladation of the triple bond, followed by... 

Aldol reaction between a ketone and an aldehyde can be controlled by prior conversion of the ketone into the ethyloxalyl derivative before reaction with the aldehyde. The keto-lactone so formed is decomposed to an alkene moiety with base. This method is particularly well suited to the formation of a-alkylidene-cyclo-alkanones (ring size >6) and a-alkylidene-y-lactones (Scheme 73). ... 

Acids 209, prepared by hydrolysis of MBH adducts with KOH, have been subjected to lactonization under the promotion of various sulfonyl chlorides, affording a-alkylidene-p-lactones 210 in moderate yields when the R group was an alkyl substituted one While R was phenyl or p-methylphenyl group, aryl allene 211 was obtained as the sole product in low yield. However, for 2091, bearing a nitro group on the phenyl section, lactone 2101 was obtained in 46% yield without the formation of aryl allene. 

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