Cyclopentenone annelation

Cyclopentenone annelation. The reaction of the dilithio derivative (2) of dimethyl 4-cyclohexene-1,2-dicarboxylate (LDA, THF/HMPT) with 1 at -45 -> 0° results in the bicyclic enone 3 in 72% yield. The reaction may involve conjugate addition of 2 to 1 to give a ketene (a) with loss of lithium phenoxide. Several other... 

This reaction has been successfully applied to cyclopentenone annelation onto cycloalkenes. By modifying Danheiser s protocol [15], alkynyl-substituted bi-cyclo[n.l.0]alkanol derivatives are prepared by the reaction of gem-lithio-bromocyclopropanes 27 with alkynylborons, as shown in Scheme 10. 

As dibromocyclopropanes can easily be synthesized by reacting a cycloalkene with bromoform in the presence of a base [16], this method affords an alternative procedure for cyclopentenone annelation onto cyclic alkenes. It should be noted that in the Pauson-Khand reaction, which is probably the most direct cyclopentenone annelation reaction, the reaction using cyclohexene gives the product only in very low yield [11,17]. Also, the position of the original alkynyl substituent on the product double bond is opposite to that in the present reaction. Thus the two reactions are complementary. 

Cyclopentenone annelation (cf. 10,444). The reagent undergoes a Nazarov-type cyclization with an a,/S-unsaturated acid chloride to give an annelated 3-phenylthio-cyclopentenone. This reaction was used to prepare the bicyclic cyclopentenone 3, a useful intermediate in synthesis of cyclopentenoid natural products, such as hirsutene (4).3... 

Assereg, J.H., Glase, S.A., and Welch, S.C. 1987. 3-Chloro-2-[(diethoxyphosphoryl)oxy]-l-propene a new reagent for a one-pot cyclopentenone annelation. Synthesis of desoxyal-lethrolone, cw-jasmone, and methylenomycin B. Journal of Organic Chemistry, 52(8) 1440-50. 

This reaction was used for an iterative cyclopentenone annelation in a synthesis of A " - -capnellene (2), formulated in part in Scheme (1). 

Cyclopentenone annelation. Enolates condense with 1 in an alkylation-intramolecular Wittig reaction sequence to afford cyclopentenones (yields, 14-39%). 

Cyclopentenone annelation. A typi cal example for use of 1 for synthesis of cyclopentenones is illustrated for annelat ion of cyclohexanone (equation I). 

Cyclopentenone annelation, The isomeric adducts 1 of 2-methylcyclohexanone and propargyi alcohol both cyclize regiospecifically to the hydrindanone 2 (70%... 

Regiospecific cyclopentenone annelations vinylsilane-terminated annelations... 

Vinylsilanes (8, 491-492) aHylic alcohols (9, 340). Details are available for conversion of a ketone to a vinylsilane in which the C—Si bond has replaced the C==0 group (enesilylation). The reaction affords the less substituted vinylsilane in the case of unsymmetrical ketones. The paper includes details for use of vinylsilanes for cyclopentenone annelation by Friedel-Crafts acylation with acryloyl chlorides and subsequent cyclization of penladienyl cations (9,498-499).1... 

Cyclopentenone annelation.7 A new method for this reaction involves Pd(0)-directed C-alkylation of 2-methyl-l,3-cyclopentanedione or 2-methyl-l,3-cyclohexa-nedione with 2-ethoxy-3-acetoxy-l-propene followed by an intramolecular Wittig reaction (equation I). Of special interest, the cyclopentenone 1 can be obtained in optically active form by use of an optically active phosphine. Thus use of (R)-DIOP (4, 273 5, 360 361 6, 309) leads to 1 as a 70 30 mixture of ( + )- and ( —)-enantiomers. Similar results are obtained with (R)-(-)-methylphenylpropyl-phosphine. 

Reaction of (50) with alkyl halides gives exclusive a-alkylation. With aldehydes and ketones, a-addi-tion again takes place to give (52) via intramolecular silyl transfer with concomitant loss of lithium cyanide (c/. 25 Scheme 30). Treatment of (52) with p-Ts0H H20 gives the cyclopentenone annelation product. The allylic cyanohydrin anion (53) also gives a-adducts upon treatment with aldehydes and ketones at -78 °C, whereas reaction with electrophiles at 0 C affords -y-adducts (c/. 25). 

Cyclopentenone annelation. Smith has extended the acid-catalyzed decomposition of diazomethyl ketones see Trifluoracetic acid, this volume) to the synthesis of bicyclopentenones. Thus treatment of the 3,7-unsaturated diazomethyl ketones (1) and (3) with BF3 (C2Hs)2 0 in nitromethane at 25° for... 

A cyclopentenone annelation of an allyl sulphide has also been reported (Scheme 19). 76... 

The present procedure is applicable to both cyclic and acyclic ketones, but is particularly useful for cyclopentenone annelation. 

The method can be used for cyclopentenone annelation of cycloalkanones, as shown in the second example. 

Condensation Reactions.—Trost has reviewed the preparation and synthetic uses of cyclopropyldiphenylsulphonium ylides. The regioselectivity and chemospecificity of the cyclopentane and cyclopentenone annelation reactions have been examined. Whereas diphenylsulphonium methylide does not cyclopropanate simple, unactivated olefins such as tetramethylethylene, transfer of a methylene group from the ylide can be effected stereospecifically in the presence of a copper catalyst and this reaction may provide a model for biological cyclopropanations by the ylide derived from S-adenosyl-methionine. Attempts to catalyse a similar transfer to unactivated olefins using PdCl2 were not successful. ... 

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