Intramolecular diels-alder reactions of indoles

The first examples of intramolecular Diels-Alder reactions on indoles indicate that this reaction may be employed for the direct preparation of highly functionalized dihydroindoles. The hybridization of the atoms in the tether plays a crucial role.     

Intramolecular diels-alder reactions of sulphonyl-substituted trienes

The synthesis and intramolecular Diels-Alder reactions of sulphonyl-substituted trienes 1 and 2 are described. The stereoselectivities of the cycloadditions are discussed, and some reactions of the bicyclic products are reported.     

Intramolecular diels-alder reactions of 1,3,8-nonatriene and 1,3,9-decatriene

The stereoselectivities of the title reactions have been investigated from 140–340°C, and relative activation parameters for $\text{cis}$ and $\text{trans}$ product formation have been determined.     

Intramolecular diels-alder reactions. 4. Additions to naphthalene

N-Methyl-N-2-propynyl-1-naphthalenecarboxamide, N-methyl-N-2-propynyl-1-naphthaleneacetamide, and N-methyl-N-3-butynyl-1-naphthalenecarboxamide undergo intramolecular Diels-Alder reactions at 190°, 250°, and 270° to give lactams 1,6 , and 9 , respectively. The cyclization temperatures are higher by 80-120° as compared to those of the corresponding anthracene derivatives. Elaboration of lactam 6 gave the trans-4a-aryldecahydroisoquinoline derivative 7a which, as the (-) isomer, was shown to have the same absolute stereochemistry as morphine.     

Asymmetric diels-alder reactions of acrylates derived from 3-alkyl-borneols and -isoborneols

Starting from (+)-camphor the chiral alcohols 7 and 8 have been prepared; their acrylates 9 and 13 underwent TiCl₂(OiPr)₂-mediated Diels-Alder addition to cyclopentadiene with stereoface-differentiations of 66% d.e. and 94% d.e., respectively.     

Intramolecular diels-alder reactions. IX. Syntheses of N-benzylcyclolignan lactams

Four bis-unsaturated N-benzyl amides of the type where (C₂) and (C₂)' are variously trans-CH?CH and C?C groups, were synthesized and refluxed in acetic anhydride. Three of them cyclized to form N-benzylcyclolignan lactams by intramolecular Diels-Alder processes. In one case [(C₂) ? C?C, (C₂)' ? trans-CH?CH] the (C₂) unit functioned as the dienophilic moiety.     

Intramolecular diels-alder reactions of the furan diene: substituent and solvent effects

An internal Diels-Alder reaction, using furan as the diene component, formed a highly functionalized 5-membered carbocyclic ring in excellent yield. Solvent and substituent effects of this reaction were examined.     

Intramolecular Friedel-Crafts-type reactions involving N-acyliminium ions derived from glycine templates

Enantiomerically pure 4-substituted 2-aralkyl-2,4-dihydro-1H-pyrazino[2,1-b]quinazoline-3,6-diones (1b-m) in which the alkyl chain is (CH(2))(n), n = 1-3, behave as glycine templates giving by treatment with [hydroxy(tosyloxy)iodo]benzene in ethyl acetate cis-1-tosyloxy derivatives. When these compounds contain electron-rich aryl substituents with n = 2, they spontaneously cyclize through intramolecular Friedel-Crafts-type diastereoselective reactions to give penta- or hexacyclic compounds. Otherwise, they give by solvolysis cis-1-alkoxy derivatives, which in a second step, may be cyclized in acid if n = 2, 3. All these reactions must occur through N-acyliminium species in S(N)1-like mechanisms. 1-Alkoxy-2-arylmethyl derivatives are reluctant to cyclize, giving trans-1-hydroxy compounds as the only isolated reaction products.     

Intramolecular diels-alder reactions of diester-tethered trienes. synthesis of medium ring-containing carbocycles and heterocycles

Intramolecular Diels-Alder reactions of cyclohexane-1,2-dicarboxylic anhydride-derived diester-tethered trienes are described. The stereoselectivities of most of the cycloaddition processes studied may be rationalised in terms of an preferred ‘inside’-oriented diene giving rise to an endo-transition state.     

Intramolecular diels-alder reactions of benzynes application to the total synthesis of mansonone E

Substituted benzynes san be trapped intramolecularly by an attached furan moiety and such a reaction has been used in the synthesis of the naturally occurring o-naphthoquin- one mansonone E.     

Intramolecular diels-alder cycloadditions of bis-diene substrates

Unique internal competition in the intramolecular cycloaddition of bis-diene substrates occurs with high stereoselectivity. Aqueous reaction conditions promote coiling of the lipophilic chain which alters the observed regioselectivity.     

Intramolecular diels-alder reaction of iminothiol esters

Diels-Alder reaction of dienyl α-methacrylthioimidates has been investigated under thermal or Lewis acid or protonic acid catalysed conditions. The utility of the reaction is shown by desulfurative ring contraction of bicyclo[4.4.0] to bicyclo[4.3.0]system.     

Intramolecular anionic diels-alder reactions of 1-aryl-4-oxahepta-1,6-diyne systems in DMSO

Base-promoted cycloaddition reactions of 1-aryl- or 1-aryl-7-substituted-4-oxahepta-1,6-diyne systems in DMSO have proven to involve an anionic intramolecular Diels-Alder process taking place even at room temperature in spite of the reaction suffering from temporary disruption of aromaticity. Although initially formed alpha-arylallenide anion can be protonated by DMSO, it can be back to the allenide anion probably because of a small acidity difference between alpha-arylallene and DMSO. The alpha-arylallenide anion in combination with the alpha-aryl substituent can constitute an anionic diene structure that undergoes the intramolecular Diels-Alder reaction involving the C(6)-yne part, a very fast process probably because of the increased HOMO-1 level of the anionic diene, as shown by DFT calculations. Diversified substituted naphthalenes, benzofurans, phenanthrenes, and quinolines, including biaryl architectures, are available from 4-oxahepta-1,6-diynes in a highly expeditious way.     

Intramolecular diels-alder reactions of dienamines with acrylates: trends in stereoselectivity upon substitution.

Intramolecular Diels-Alder reactions of all-$\text{trans}$ ethyl 10-diethylamino-2,7,9-decatrienoate and 11-diethylamino-2,8,10-trienoate occur readily to produce $\text{trans}$ and $\text{cis}$-fused products in ratios of 85:15 and 55:45, respectively.     

Propellanes-LV : Synthesis and diels-alder reactions of tetraenic propellane imides derived from esters of α-aminoacids

Tetraenic propellane imides were prepared from a variety of α-aminoesters. The extent to which these were attacked by 4-substituted-1,2,4-triazolinediones from the side syn or anti to the imide ring was in most cases determined by the size of the substituent in the imide ring although some exceptions occur.     

Polylactones derived from polymethacrolein and styrene–methacrolein copolymerizations

Emulsion polymerization of methacrolein produces a polyacetal which can be converted through the action of sodium hydroxide to an alternating copolymer of methallyl alcohol and sodium methacrylate. Support for the alternating structure was gained primarily through a study of the polylactone formed through subsequent acidification of the sodium salt. Thus, the poly(methallyl alcohol–sodium methacrylate) copolymer was acidified under selected conditions to give a soluble polylactone containing 14.2 mole-% of residual acid and hydroxyl groups. This number agrees quite closely with the value of 13.5 mole-% which one would predict from the random cyclization of a true alternating copolymer. Cyclization of a random copolymer of poly(methallyl alcohol–sodium methacrylate) in a random fashion would have resulted in a value of about 36.8 mole-%. The results also support both the 1,2 vinyl polymerization of methacrolein and a nonrandom attack of the polymethacrolein by base. In a completely separate set of experiments, the value of r₁ and r₂ for the copolymerization of styrene (M₁) and methacrolein (M₂) were determined to be 0.22 ± 0.02 and 0.88 ± 0.02, respectively.     

Intramolecular diels-alder reactions. XI. Modal selectivity in the syntheses of some parent cyclolignan lactones

Ph(C₂)CH₂Cl and Ph(C₂)'CO₂Na [where (C₂) = -C=C- or trans-CH=CH-, (C₂)' = -C=C- or cis-CH=CH-] reacted in refluxing dimethylformamide to yield unsaturated esters Ph(C₂)'CO₂-CH₂(C₂)Ph and/or their intramolecular Diels-Alder cyclization products (cyclolignan lactones). It was found that modal selectivity for cyclization in DMF sometimes varies from that found previously with acetic anhydride as solvent. Two new parent tetrahydrocyclolignan lactones were synthesized.     

Type-Two intramolecular diels-alder reactions of pyrazolo-o-quinodimethanes

Two isomeric series of homologous N-(acryloyloxy)alkylated pyrazolo-3-sulfolenes 10a-c and 18a-c have been efficiently synthesized from a common starting material, 4,6-dihydro-1H-thieno[3, 4-c]pyrazole (5). Thermolysis of these fused 3-sulfolenes provides the corresponding o-quinodimethanes which simultaneously undergo "type-two" intramolecular Diels-Alder reactions to form two- and three-atom-bridged tricyclic pyrazoles which are otherwise difficult to prepare. It was also demostrated that, depending on the N-substitution position of the pyrazolo-fused 3-sulfolenes, the temperature required for the thermal extrusion of SO(2) and the regioselectivity of the T2-IMDA reactions were influenced substantially.     

Stereoselective diels-alder reactions of chiral anthracenes

Various chiral (9-anthryl)carbinol templates undergo Diels-Alder cycloadditions with a variety of symmetric and nonsymmetric dienophiles with excellent pi-facial selectivity and regioselectivity, under both thermal and Lewis acid catalyzed conditions.