Tetralin cyclization

TABLE 9. Synthesis of Tetralines Cyclization of l-Halo-2-pentenylarenes and Related Componnds... 

A similar intramolecular alkylation of arene-ene substrates is catalyzed by RuGl3/AgOTf, providing good to excellent yields of cyclization products (chromanes, tetralins, terpenoids, and dihydrocoumarins).25 This method is applied to the synthesis of tricyclic terpenoids, which are formed in nearly quantitative yields with high stereoselectivities (trans cis various between 99 1 and 99 2), as shown in Equation (24). 

Intramolecular process with rhodium catalyst has been described for the syntheses of indane, dihydroindoles, dihydrofurans, tetralins, and other polycyclic compounds. Wilkinson catalyst is efficient for the cyclization of aromatic ketimines and aldimines containing alkenyl groups tethered to the K z-position of the imine-directing group. 

Cyclization of diethyl N-[cyclohepta(6)pyrrrol-2-yl]aminomethylene-malonates (1676), by heating in xylene, t-butylbenzene, or tetralin at reflux temperature, gave cyclohepta[4,5]pyrrolo[l, 2-a]pyrimidine-3-carboxyl-ates (1677) in 46-90% yields (87BCJ1053). Cyclization were also carried out in a mixture of phosphoryl chloride and polyphosphoric acid. While compound 1676 (R = COOEt) gave 1677 (R = COOEt) in 95% yield, the unsubstituted 1676 (R = H) afforded a mixture of 1677 (R = H) and 4-hydroxycyclohepta[4,5]pyrrolo[2,3-b]pyridine-3-carboxylate (1678) in 7% and 48% yields, respectively. The nitrogen bridgehead compound (1677, R = H) could not be transformed into pyridine derivative (1678). 

The retrosynthetic concept of the Nicolaou group is shown in Scheme 22. The target molecule 36 is disconnected via an IMDA cyclization of the diene quinone precursor 138, which would be generated from the tetraline derivative 139 using Wittig chemistry followed by aromatic oxidation. A Claisen-type rearrangement would provide access to 139 whereby the side chain required for the rearrangement of 140 would be introduced by 0-acylation. The core of 141 would be formed via an intermolecular Diels-Alder reaction between diene 142 andp-benzoquinone 130 [42]. 

The cyclization of this by Bischler-Napieralski method, using phosphorous oxychloride, gives 3,4-dihydropapaverine (19.4.6), which is dehydrated into the desired papver-ine when heated in tetraline at high temperatures [28-31]. 

Synthesis of a m-decalin system by the asymmetric cyclization[38] has been carried out with high enantioselectivity[142,143,147,148], Using BINAP as a chiral ligand, 91% ee was achieved in the asymmetric cyclization of 177 to give 178. In order to achieve an efficient asymmetric cyclization, selection of the reaction conditions is crucial, and sometimes added Ag salts play an important role[148], A catalytic asymmetric cyclization of 179 to prepare the key intermediate enone 180 for vernolepin synthesis has been carried out[149]. Highly efficient asymmetric cyclization of 181 to give the tetralin system 182 has been applied to the synthesis of (-)-eptazocine (183)[150], Hydrindans are synthesized in 86% ee[151]. 

Tetralins indanes. P205 can be used for cyclodehydration for substrates such as 1-aryl-l-pentanols or 2-aryl-2-hexanols. In the case of secondary alcohols, yields are sometimes improved by dehydration with TsOH to a styrene followed by cyclization with P2O5.1 The product of the second example is a known sesquiterpene, calamenene. 

Cyclization to five-membered rings forms the alkylindans and indenes cyclization to six-membered rings gives tetralins and naphthalenes. Tetralins and decalins, however, were not observed in any of the experiments, because of unfavorable equilibrium. For example, less than 0.02-0.1% tetralin and less than 0.001% decalins would be expected if they were in equilibrium with the naphthalene formed in the n-butylbenzene experiments. [Equilibrium conversions calculated from the data of Egan (15), Allam and Vlugter (16), and Frye and Weitkamp (17)]... 

C5- and C6- cyclizations are parallel reactions. Csicsery has shown that isomerization of tetralin to methylindan over platinum-alumina at 371°C is extremely slow (22). Davis and Venuto provided further evidence by showing that methylindan is also not converted to tetralin or naphthalene over platinum on silica-alumina (23). This behavior is similar to that observed in the cyclization of aliphatic hydrocarbons. Davis and Venuto also reported that the major aromatic products obtained from ten C8-C9 paraffins and olefins at 482°C are only formed by direct six-membered ring... 

In an application of this strategy to the synthesis of (-)-eptazocine, substrate 9.5 was cyclized under optimized conditions to furnish Heck product 9.6 in excellent enantioselectivity (Scheme 8G.9). Tetralin 9.6 was subsequently converted in several steps to (-)-eptazocine (9.7) [22],... 

Hirano et al. reported on the stereoselective cyclization to give tetralin derivatives using the phenanthrene-p-dicyanobenzene sensitizer system. Pandey independently reported the intramolecular photocyclization of methoxybenzene derivatives bearing silyl enol ether chromophore via their heterodimer radical cations in the presence of 1,4-dicyanonaphthalene gave benzo-annulated cyclic ketones in 70% yields [490] (Scheme 133). 

The highly efficient asymmetric cyclization of 97 using (i )-BINAP as a chiral ligand based on the differentiation of enantiotopic faces gave the tetralin system 98 with 93% ee and has been applied to the synthesis of (—)-eptazocine (99) [45]. 

The use of co-(2-bromophenyl)alkyl-2-oxazolines (13) in base-promoted ring-closure reactions provides a good access to 1-phenyl-indane and 1-phenyl-tetralin derivatives (14) that contain easily manipulated oxazoline moieties. Satisfactory isolated yields of cyclized products 14 are obtained with lithium diisopropylamide (LDA) in THF at room temperature under irradiation with UV light, even when quaternary centers are formed (Scheme 10.39) [55]. The yield of 14 (n= 1, R= Ph) increases to 75% when the reaction proceeds under laboratory light for 48 h at room temperature. 

If an [Os]-anisolium complex bears a proton at C4 (63, Scheme 7), exposure to DIEA at low temperature results in a kinetic deprotonation of the benzylic carbon attached to C3 generating the extended vinyl ether 64. This complex cyclizes under Lewis addic conditions to generate an anisolium ion, which can then be deprotonated at C4 to generate a tetralin complex [25]. Heating this species liberates the tetralin 65 in 39 % yield (based on 63). 

These authors have extended this reaction to the preparation of 3-substituted benzocy-clobutenes 283 (n = 1) and 5-substituted tetralins 283 (n = 3) from a-(2-fluorophenyl)-tw-iodoalkanes 282. In a similar way as described above, the processes involve generation and cyclization of benzyne-tethered alkyllithiums via 4-exo or 6-exo, though in these cases the yields are significantly lower (Scheme 74)132. 

The ene hydrazine 100, prepared from dimedone and methylhydrazine, forms the Michael adduct 101 with dimethyl acetylenedicarboxylate. The adduct is converted into a mixture of pyrrole and pyridone derivatives, 103 and 104, in boiling tetralin. These products arise by a [3.3]sigmatropic shift in the adduct with cleavage of the nitrogen-nitrogen bond to give 102, followed by cyclization and elimination of ammonia and methanol, respectively (equation 42)63. 

This type of cyclization is not limited to propanediones but has also been observed with ortho substituted benzils104) and with tetralin derivative 149. In the latter case, a cyclic sulfone was also obtained in quantitative yield. 

Azido-5-formyl-l,3-dimethyluracil is cyclized with hydrazines to afford pyrazolo[3,4-reaction with triphenylphosphine in benzene result in the formation of isoxazolo[3,4-c/]pyrimidine and pyrimido[4,5-[Pg.182]

Indan (265, n = 3) and tetralin (265, n = 4) derivatives are obtained from 1,6-heptadiyne or 1,7-octadiyne with simple alkynes in the presence of CpCo(CO)2, and although the yields are not high (14-50%) the products are easily obtained pure by column chromatography""". The synthetic applications of these cyclizations have been reviewed recently""". ... 

There are a few tetra- and pentacyclic analogues. Benzo analogues of 245 were prepared from pyridine-2,3-dicarboxylic acid anhydride and a tetralin derivative under conditions of the Friedel-Crafts reaction (85JCR(S)338). Pentacyclic compounds 258 (R = H or Me) were prepared from the bis adduct of anthranilic (or IV-methylanthranilic) acid to 1,4-benzoquinone, followed by cyclization in concentrated sulfuric acid (55JCS4440 66CB1991). 6-Methylquinoline-5,8-dione dimerized in the presence of ethanolic N-methyl-cyclohexylamine to 259 in very low yield and the dimerization is interpreted as two base-catalyzed addition reactions and three oxidation steps (71JCS(C)1253). 

In general, carbonyl groups do not function as good initiators in vinylsilane-mediated cyclization reactions and relatively few examples exist. The cyclization of vinylsilanes with ketones or aldehydes as initiators is a highly underdeveloped reaction that holds considerable potential. As reported by Tius and coworkers, treatment of aldehyde (13) with a catalytic amount of p-toluenesulfonic acid gave a mixture of the tetralins (14) and (15) in a combined yield of 53%, with lesser amounts of the enone (16 Scheme 8). The enone system presumably arises from the intramolecular 1,3-hydride transfer of the intermediate a-silyl carbocation (17). Similarly, the vinylsilane (18) undergoes cyclization to produce the disub-stituted benzene derivative (19), although yields are low. 

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