Bicyclo enones

The photocycloaddition of cyclo-olefins to cyclic aP-unsaturated ketones has been used in propellane synthesis. Thus, (837) was prepared by addition of cyclohexene to the relevant bicyclo-enone, and (838) was likewise prepared from A -octalin and... 

Cyclohex-2-enone- bicyclo [3.1.0] hexan-2-one rearrangement, 318 3a,5o -Cyclo-6/3,19-oxidocholestane, 268 18,20-Cyclo-5a-pregnane-3, 20-diol 3-acetate, 264... 

Photochemical cyclohex-2-enone bicyclo (3.1.0)hexan-2-one rearrangement, 320 Photochemical a-cyclopropyl ketone isomerization, 313... 

Karl R. Dahnke and Leo A. Paquette 181 INVERSE ELECTRON-DEMAND DIELS-ALDER CYCLOADDITION OF A KETENE DITHIOACETAL. COPPER HYDRIDE-PROMOTED REDUCTION OF A CONJUGATED ENONE. 9-DITHIOLANO-BICYCLO[3.2.2]NON-6-EN-2-ONE FROM TROPONE... 

Me. A third possibility would be that the a-chloroenolate intermediate, which is a carbenoid, would a-eliminate a chloride ion to yield carbene 229, which would subsequently intramolecularly cycloadd onto the double bond of the enone moiety. When = H, Me as in 231 a, b, reductive cleavage of the C - bond (e.g. with lithium in liquid NH3) can produce bicyclo[2.2.2]octane derivatives 230. The... 

Starting from optically active 1-chlorovinyl p-tolyl sulfoxide derived from 2-cyclohex-enone, the asymmetric synthesis of cyclopropane derivative (85) was realized (equation 23) . Addition reaction of lithium enolate of tert-butyl acetate to 83 gave the adduct (84) in 96% yield with over 99% ee. Treatment of the latter with i-PrMgCl in a similar way as described above afforded optically pure (15,6/ )-bicyclo[4.1.0]hept-2-ene (85) in 90% yield. 

The photoisomerization of 2-(pent-4-enyl)-3-oxycyclohex-2-enones 5 to 6-oxytricyclo[6.3.0.01,6]-undecan-2-ones 6 has been used as a key step for the synthesis of sesquiterpenes containing the bicyclo[6.3.0]undecane carbon skeleton.15 16... 

Among bicyclic cyclohex-2-enones, the formation of tricyclo[4.4.2.01,6]dodecane-2,7-dione from bicyclo[4.4.0]dec-l(6)-ene-2,7-dione and ethene proceeds in 95% yield,101 and that of 8-mcthyl-tricyclo[6.4.0.01,4]dodecan-5-ones from 6-methylbicyclo[4.4.0]dec-l(2)-en-3-one and ethene in 77% yield,102 respectively. Steroids containing cyclohex-2-enone subunits,103 e.g. 17/ -acetoxy-5a-androst-1 -en-3-one,104 often afford /raw-fused cycloadducts with alkenes. When such reactions are performed on silica gel, complete reversal of stereochemistry to that observed in solution can occur.105... 

Bicyclo[3.2.0]heptan-6-ones 10 were obtained by transformation of 2-methoxycyclohex-2-enones 8 to l-methoxybicyclo[4.1.0]heptan-2-ols 9 and subsequent rearrangement (Table 13).155 161 For the synthesis of the requisite precursors, a sequence of reduction and cyclopropanation 8 - 9, eventually followed by oxidation and an addition to the carbonyl group 9 — 11 — 12, proved most effective. 

In terms of the bicyclo[3.1. OJhexenyl ions, the structure of the protonated ketone 65 was determined by Childs, Lock and colleagues60. The bond distances associated with the protonated carbonyl group and unsaturated portion of 65 were completely consistent with those expected for a protonated enone (Table 5). However, comparison of the cyclopropyl portion of structure 65 with that of the 2-hydroxyhomotropenylium ion (vide supra) and... 

Majetich reports that the fluoride ion catalyzed carbocyclization of ally anion equivalents to a, 3-enones is sensitive to the structure of the a,p-enone in which competing 1,2- and 1,4-addition processes occur.116 For example, a,(3-enones (135) afford predominantly the jyn-bicyclo[4.3.0]nonan-3-ones (136)... 

Majetich reports a general intramolecular Lewis acid allylation protocol for the synthesis of bicy-clo[5.4.0]undecen-3-ones (168) and bicyclo[4.4.0]decen-3-ones (170), which are 1,6-addition products (Scheme 27). The same precursors, (167) and (169), when submitted to the fluoride ion cyclization protocol, also afford 1,2- and 1,4-addition products.73 Typically, ethylaluminum dichloride, a proton sponge Lewis acid, is used in order to minimize adventitious protonic desilylation. Other 0,y-unsatu-rated silanes also undergo similar intramolecular Lewis acid catalyzed additions for example, the si-lylpropargylic enones (171) undergo intramolecular cyclization to the allenylspiro system (172).74... 

In the Weiss reaction (Scheme 4), an 7-dicarbonyl compound (38) condenses with two molecules of dimethyl 3-oxoglutarate (39 E = CC Me) to give a c w-bicyclo [3.3.0] oct-ane-3,7-dione tetraester (40) the one-pot reaction produces considerable complexity, with the sequential formation of four C—C bonds. Simple acid treatment removes the carbomethoxy groups, if deshed. While die reaction involves aldol and Michael sequences, die intermediacy of a cyclopentenone [4-hydroxycyclopent-2-enone (41)] has up to now been unproven. A series of such 1 1 adducts has now been reported for a variety of diketones, together with evidence diat diey are indeed intermediates en route to the bicyclo system.62 Electronic and steric effects on the reaction are also discussed in detail. 

The normally sluggish Diels-Alder cycloaddition between cyclohexa-1,3-diene and various enones and enals can be activated by precoordination of the diene to a jt-basic molybdenum complex TpMo(NO)MeIm(//-cyclohexadiene)].134 The 4-1-2-cycloaddition of cyclohexa-2,4-dienones with electron-deficient 2n -dienophiles produced bridged bicyclo[2.2.2]octenones. Triplet-sensitized irradiation of these bridged bicyclooctenones produced bicyclo[3.3.0]octanoids, whereas direct irradiation yielded bicyclo[4.2.0]octanes.135... 

Known bicyclo[4.3.1]enone 15758 was converted into vinylsilane 158 with bis(trimethylsilyl)methyl lithium.55 Diene 158 underwent selective ozonolysis at the cis-olefin under conditions to produce differentially oxidized termini 90 alde-hydo-ester 159 was homologated with a phosphine oxide anion91 to enol 160. Subsequent hydrolysis of 161 provided substrate 162, which after tandem ozonolysis-acidification gave racemic 6,9-desmethyl analogue 155. Unfortunately, initial efforts failed to resolve 155 into its two optical isomers with cellulose triacetate.92 However, the antimalarial activity of racemate 155 is intriguing, as discussed in a later section. 

The intermolecular Diels-Alder reaction between the dibromoenone (111) and dienes (112) provides access to bicyclo[5.4.0]undecane systems (113) that are common core structures of many natural products (Scheme 32).118 The alio-threonine-derived O-(/ -biphenyl carbonyl oxy)-/i-phenyloxazaborolidi none catalyses the enan-tioselective Diels-Alder reaction of acyclic enones with dienes.119 The reversal of facial selectivity in the Diels-Alder cycloaddition of a semicyclic diene with a bro-moenone was induced by the presence of the bromo substituent in the dienophile.120 Mixed Lewis acid catalyst (AlBr3/AIMe3) catalyses the Diels-Alder reaction of hindered silyloxydienes with substituted enones to produce highly substituted cyclohexenes.121 Chiral /V-enoyl sultams have been used as chiral auxiliaries in the asymmetric Diels-Alder reactions with cyclopentadiene.122... 

In the preparative application of [2 + 2]-photocycloadditions of cyclic enones to (substituted) alkenes, two factors concerning product formation are of decisive relevance, namely the regioselectivity and the (overall) rate of conversion. Regarding the regioselectivity in the addition to mono- and 1,1-disubstituted alkenes, Corey had shown that the preferred addition mode of cyclohex-2-enone to isobutene or 1,1-dimethoxyethylene was the one leading to—both cis- and trans-fused—bicyclo[4.2.0]octan-2-ones with the substituents on C(7) [8]. In contrast, in the reaction with acrylonitrile, the alternate orientation was observed to occur preferentially. Similar results were also reported by Cantrell for the photocycloaddition of 3-methyl-cyclohex-2-enone to differently substituted alkenes [14]. No significant differences in the overall rates of product formation for the different alkenes were observed in these studies. In order to explain these observed... 

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