Decalin, acylation

The isoquinoline framwork is derived from the corresponding acyl derivatives of P-hydroxy-P phenylethylamines. Upon exposure to a dehydrating agent such as phosphorous pentaoxide, or phosphorous oxychloride, under reflux conditions and in an inert solvent such as decalin, isoquinoline frameworks are formed. 

Thermolysis of the 3-acyl-3/f-azepine 32 in Decalin at 250°C also gives the phenacylpyridine but in much reduced yield (6%). In a similar manner, 4-chloro-yV,/V-diethyl-3-phenacylpyridin-2-amine (53 % bp 160 C/0.18 Torr) is produced by the photolysis or thermolysis of 3-benzoyl-5-chloro-Ar,Ar-diethyl-3/f-azepin-2-amine.246 However, if the 3ff-azepine bears a secondary amine residue at the 2-position, e.g. 36, then photolysis or thermolysis yields a pyrrolo[2,3-/>]pyridine by intramolecular cyclization of the 3-phenacylpyridin-2-amine intermediate. 

Intermolecular acylation of 3,4-dimethoxyphenylacetic acid occurs in polyphosphoric acid, leading to 2-(3,4-dimethoxyphenylacetyl)-4,5-dimethoxyphenylacetic acid (622). Cyclization to the isochromanone takes place when the keto acid is heated in decalin (Scheme 240) (72JHC853). 

The azabicyclononane system is a common structural feature in diterpene alkaloids, and the nitrene insertion route to the ring system has been studied in detail in model decalins as well as in steroids (Scheme 11). Thus irradiation of the rrans-acyl azide (21) gave, in addition to isocyanate (30-33%), a mixture of Ae 7- and 8-lactams (22) and (23). The y-lactam (22) predominated, dthough the overall yield was poor. > The corresponding c/s-azide (24), however, gave the 8-lactam (25) as Ae major product, again in low yield. One elegant application of this type of intramolecular nitrene insertion reaction... 

Intramolecular acylation. This reaction is the key step in a new synthesis of the twistane ring system By a Canadian group.14 The starting material, decalin-2,7-dione (3), can be prepared easily in quantity by hydrogenation of 2,7-dihydroxynaphthalene to a mixture of isomeric diols (2) and chromic acid oxidation of the mixture.15 16 Treat-... 

In the realm of synthesis, two groups74,75 have reported a facile preparation of the 3-isoquinolone derivative (40) by the same method, and one of these has used this compound as an intermediate for entries into tetrahydropapaverine (41 R = H) and ( )-laudanosine (41 R = Me) as shown in Scheme 3.75 Inter-molecular acylation of 3,4-dimethoxyphenylacetic acid with polyphosphoric acid gave (39) in 60 %75 or 95 %74 yield. The latter compound was readily converted into tetrahydropapaverine (41 R = H) in three steps. On the other hand, treatment of (42), prepared by dehydration of (39) in refluxing decalin, with methylamine followed by identical steps to those used in the synthesis of (41 R = H) gave (+)-laudanosine (41 R = Me). 

Oxazoles. Acylation and pyrolysis of the hydroxy amides in decalin provides 2-substituted oxazoles by way of cyclodehydration and retro-Diels-Alder reaction. Imidazoles are similarly prepared from the vic-diamine. 

Z)-2-Acyl-2-enals are readily prepared by retrocycloaddition of 5-acyl-4-alkyl-4W-1,3-dioxins <01JA9455> and cts-fused decalins are accessible by reduction of the intramolecular photo-product from 2-cycloalkenyl-l,3-dioxin-4-ones <01H(54)765>. 

Significant differences in the acetylation of naphthalene with acetic anhydride (2 1 molar ratio) over HBEA are observed with decalin or sulfolane as solvents the diffoent hydrophilicities of these solvents dramatically inflnence the resulting naphthalene conversion. The hydrophilic sulfolane into-acts more strongly with the zeolite surface, thus blocking the acid sites that are less available for the acylation reaction (naphthalene conversion = 14%) on the contrary, the hydrophobic decalin enables the adsorption of acetic anhydride and increases the rate of acylation reaction (naphthalene conversion=25%). Due to the defined structure of the HBEA, the selective formation of isoma-15 is probably achieved via a restricted transition state selectivity (15 13=81 19 at 35% naphthalene conversion). It must be underlined that different secondary products are, in general, produced on the catalyst surface due to consecutive reaction of the products. 

The 1,2-hydride ion shift in the first intermediate gives a T-carbo-cation which cyclizes into tetrahydrofuran derivatives. This process is observed during the acylation of decaline (vide infra). 

On the other hand, Baddeley showed in 1961, that the acylation of decaline gave a mixture of products containing 5. have studied this reaction and observed... 

Tsuge et al. found that acylation with a-ketoisocyanates, while initially affording the expected amido-ylide, presented the possibility of furth intramolecular reaction to afford an oxazole (in the case of benzoyl isocyanate) or a thiazole (in the case of thionobenzoyl isocyanate). In the latter case, the initial acylation product could not be intercepted, the thiazole being obtained, and in the former case the oxazole could be obtained by heating in decalin. 

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