1.2.3.4- Tetrahydroisoquinoline, oxidation preparation

Diels-AIder reactions were utilized to prepare isoquinoline derivatives. Various tetrahydroisoquinoline-3-carboxylic acid derivatives were prepared by an enyne metathesis followed by a Diels-AIder reaction. For example the enyne 71 was treated with Grubb s catalyst to afford diene 72 in 65% yield. Subsequent Diels-AIder reaction and oxidation gave tetrahydroisoquinoline 73 in 93% yield <0OCC5O3>. Dihydrosoquinoline 75 was prepared... 

Another cyclic derivative, 1-t-butylperoxy-benziodoxole, was easily prepared and stable it showed good oxidizing properties, for example, it oxidized diphenylsul-phide to its sulphoxide (84%) at room temperature (other reagents failed to react under these conditions) and it dehydrogenated 1,2,3,4-tetrahydroisoquinoline to 3,4-dihydroisoquinoline (83%) [11]. 

Dehydrogenation. CuClj is an efficient reagent for the preparation of pyridazinoneS from the dihydro compounds. Dehydrogenation of 1,2,3,4-tetrahydroisoquinolines to give the 3,4-dihydro derivatives is achieved under high pressure of oxygen." Substituted dibenzofurans are formed by an intramolecular oxidative coupling of o,o -dilithiodiaryl ethers with CuClj. 

The first examples of the 1,3-oxazete system (44) have been prepared by the sequence shown in Scheme 8. The first stable 4-imino-l,2-oxazetidines (45) have been obtained from [3 + 1] cycloaddition of isocyanides to N-neopent-ylidene-t-butylamine AT-oxide. Their chemistry is dominated by O—N bond cleavage for example, acid brings about rearrangement to amino-acid derivatives, and, in the presence of tetrahydroisoquinoline, cyclo-reversion to give imine and isocyanate can be detected. An unstable 1,3-oxazetidine is involved in the reaction of the imine (46) with the aldehyde (47) to give the imine (48). ... 

Azafluroanthenes were prepared via three steps Pictet-Spengler production of the tetrahydroisoquinoline, followed by microwave-induced direct arylation, and finally deprotection/oxidation (Scheme 81) (13EJO1107).The arylation step is robust enough to tolerate a wide range of substituents—both electron-donating and electron-withdrawing.This approach provides a rapid, mild route to natural products, rufescine and tricHdine. 

Tetrahydroisoquinoline 1826, a useful intermediate for the preparation of 8,11-iminoazepino[l,2- ]isoquinoline derivatives as antitumor agents, has been synthesized by a reaction sequence including a Swem oxidation [1327]. 

SCHEME 2835. Preparative oxidative C—C coupling and kinetic resolution of different racemic tetrahydroisoquinoline using... 

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