Stannic chloride ring closure

In spite of the many disadvantages, thionyl chloride has been used with considerable success in numerous cyclizations. A generally effective procedure for preparing the acid chloride involves the treatment of a dry ethereal solution of the acid with an excess of thionyl chloride and a drop or two of pyridine as a catalyst.90 By this method, in conjunction with stannic chloride and benzene for the cyclization, excellent yields of ketones (Table VI, examples without asterisks) were obtained. The ring closure of 7-l-naphthylbutyric acid affords a typical illustration of the procedure. 

In five out of six ring closures, better yields were obtained with stannic chloride than with aluminum chloride. The greater activity of the latter reagent was apparently not necessary in these instances. There... 

Stannic Chloride pn the Free Acid. Ring closure by heating the free acid with stannic chloride at 100-120° has been shown to be successful on several types of acids.85 47> 8 88 80, 189 819 These and some other acids which have been cyclized by this method may be found in Table XI. In four instances (items 3, 7, 14, 17) stannic chloride treatment gave better results than sulfuric acid. Eleven of the acids in Table XI (items 3, 5, 8, 9, 10,12, 13, 14, 16, 17, 18) have been cyclized also by the Friedel-Crafts method on the acid chloride. With seven acids (3, 6, 8, 9, 12, 14, 17) the yields were better, while with four (5, 10, 16, 18) they were lower, than with stannic chloride. Except for one (18) of these latter acids, however, there seems to be some question as to whether the optimum conditions for the Friedel-Crafts reaction were employed. Of the acids (4, 6,12) which have since been cyclized with hydrogen fluoride, considerable improvement in yields was realized. 

It may be suggested tentatively that ring closure by the action of stannic chloride on the free acid is generally inferior to both the Friedel-Crafts and hydrogen fluoride methods. Some advantages seem to be afforded, however, by the simplicity of manipulation. 

A summary of the results of the experiments on the cyclization of 7-2-phenanthrylbutyric acid may be found in Table XIV. The sharp contrast between the direction of ring closure with hydrogen fluoride (item 6) and with stannic chloride in the Friedel-Crafts-reaction (item 1) is quite striking and of obvious practical significance. Some further indications that hydrogen fluoride has an unusual influence on the ori-... 

Similar attempts to cyclize 4-amino-3-benzyl- or 4-amino-1-methy 1-5-ethoxalylaminomethyl-1,2,3-triazole (see 20) were unsuccessful. Surprisingly, 5-aminomethyl-3-benzyl- and 5-aminomethy 1-1 -methy 1-4-oxamoylamino-1,2,3-triazoles spontaneously isomerized to 4-amino-3-benzyl- and 4-amino-l-methyl-5-oxamoylaminomethyl-l,2,3-triazoles, which resisted ring closure with stannic chloride, phosphoryl chloride, or boiling butanolic sodium butoxide.69... 

Fused Azepines.—Formation. A convenient route to benzazepinones (25) in which the aryl ring has an electron-donating substituent (R) is provided by the cyclization of y-(aryl)propyl isocyanates, using phosphorus oxychloride and stannic chloride.The benzazepine-l,3-dione (27) was synthesized by ring-closure of (26) and hydrolysis of the chloroimide (28) that was formed irradiation of (27) produced mainly dimers at the alkene bond. ... 

One of the new methods studied for the building of the isoquinoline structure made use of the condensation of nitrilium salts with j3-chloro-ethylbenzene 181). It has been used for the preparation of many 3,4-dihydroisoquinolines, which can be easily dehydrogenated to the corresponding isoquinolines. 3,4-Dihydropapaverine was obtained as picrate, in 21% yield, by condensing a-chloro-j8-(3,4-dimethoxyphenyl)-ethane (CIX) with homoveratronitrile-stannic chloride (CX), a reaction which involves the ring closure of the mesomeric ion CXI (182). 

An added observation is that, when stannic chloride is made to coordinate with the sulhnyl chloride and the right amount of an oxoligand, the yield of the ring closure step is significantly improved. Examples of... 

Stannic Moridelaluminum chloride Dibenzo[a,l]pyrenes by Scholl ring closure... 

The stannic chloride-catalyzed cyclization of acyl cyclopropane (195) to the tricyclic ketone (196) affords a precedent for the biogenesis of the tricyclo[4.4.0.0 ]nucleus of copaene and ylangene 270). The reaction pathway is thought to proceed via ring opening, cyclization, hydride shift, and ring closure. 

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