Tetralins, synthesis

A related modification also involves alkenes and is called the Darzens tetralin synthesis. 1 In this process, the alkenyl group is used directly as the eation precursor. An example is 232, which was treated with concentrated sulfurie acid followed by gentle heating to give the tetralin (tetrahydronaphthalene, 233) 8 jhe only differenee between this and the Bogert synthesis is the method by which the alkenyl arene is formed. Tetralin formation from an alkenylbenzene derivative is most often referred to as the Darzens tetralin synthesis rather than the Bogert synthesis. 

A further example is given below illustrating the use of a dibasic anhydride (succinic anhydride) the succinoylation reaction is a valuable one since it leads to aroyl carboxylic acids and ultimately to polynuclear hydrocarbons. This general scheme of synthesis of substituted hydrocarbons through the use of succinic anhydride is sometimes called the Haworth reaction. Thus a-tetralone (see below) may be reduced by the Clemmensen method to tetralin (tetrahydronaphthalene) and the latter converted into naphthalene either catal3d.ically or by means of sulphur or selenium (compare Section, VI,33). 

The intramolecular variant of the Friedel-Crafts alkylation is also synthetically useful, especially for the closure of six-membered rings, e.g. the synthesis of tetraline 8 but five- and seven-membered ring products are also accessible ... 

Scheme 46. Synthesis of 3-arylisoquinoline alkaloids. Reagents a, BrCN b, CH3NH2 c, 10% KOH, EtOH d, Pd, tetralin e, NaBH3CN f, T1(N03)3, MeOH g, 5% HC1 h, H2CrOA, H2SO i, CH2N2.

Table 5.1. Synthesis of tetralines by intermolecular trapping of hydroxy-o-quinodimethanes.

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). 

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]. 

The addition of 1-lithiocyclopropyl phenyl sulfide to paraformaldehyde was the first step of an efficient synthesis of cyclobutanonc (8).169 The adduct 7 was rearranged with/Moluenesulfonic acid monohydrate in a mixture of tetralin and water while the liberated benzenethiol was trapped with mercury(II) chloride. 

Sumimoto introduced a new sebacic acid process including several catalytic hydrogenation reactions.342 The synthesis starts with naphthalene, which is first partially hydrogenated to tetralin over cobalt oxide or molybdenum oxide, then to decalin over ruthenium or iridium on carbon. The selectivity to cw-decalin is better than 90%. In a later phase of the synthesis 5-cyclododecen-l-one is hydrogenated over Raney nickel to obtain a mixture of cyclododecanone and cyclodode-canol in a combined yield of 90%. The selectivity of this step is not crucial since subsequent oxidation of either compound leads to the endproduct sebacic acid. 

Tetralins — see also Naphthalenes, tetrahydro-thermochemistry, 2, 368 Tetralones Schmidt reaction azepine synthesis by, 7, 531 Tetramisole—see Imidazo[2,I-6]thiazoie, ( )-2,3,5,6-tetrahydro-6-phenyl-... 

The addition-protonation procedure maintains the arene-chromium bond and allows further application of the activating effect of the metal. In an approach to the synthesis of anthraquinone antibiotics, the dihydronaphthalene complex (79) was allowed to react with a cyanohydrin acetal anion and then quenched with acid.129 The resulting tetralin complex (80) could be metallated effectively and carried on to a key intermediate (81) in anthraquinone construction (equation 54)... 

SYNTHESIS To a solution of 49.2 g 5,6,7,8-tetrahydronaphthol (5-hydroxy-tetralin) in 100 mL MeOH, there was added 56 g methyl iodide followed by a... 

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],... 

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