Dihydroisoquinolines, acetylenic —

In another group of (2 + 2)-cycloaddition reactions, the heterocyclic nucleus reacts via an electron-deficient carbon-carbon or carbon-nitrogen double bond with electron-rich aminoacetylenes (ynamines). For instance, thiete 1,1-dioxides, JV-benzylmaleimide, and 2,3-bis(methoxycarbonyl)-7-oxabicyclo( 2.2.1 lhepta-2,5-diene reacted with 1-diethylamino-l-propyne and with 1 -phenyl-2-( 1 -pyrrolidinyl)-acetylene to give the (2 + 2)-cycloadducts 48, 49, and 50, respec-tively.35,37,53 The latter product was thermally rather unstable, and its structure was identified on the basis of its conversion with 2,4,6-tri-methylbenzonitrile oxide into 51.53 (2 + 2)-Cycloaddition via a carbon-nitrogen double bond has been reported to take place in the reactions of 3,3-dimethyl-3//-indoles and 3,4-dihydroisoquinoline with ynamines, e.g., l-dimethylamino-2-phenylacetylene, in the presence of boron trifluoride.54 The (2 + 2)-cycloadducts 52 and 53 were not isolated, but... 

Activation of Carbon-Carbon r-Bonds. The title compound can form adducts with unpolarized jr-systems, allowing the addition of soft nucleophiles. The addition of /3-dicarbonyls onto alkynes is the most reported instance of this type of reaction, with both intramolecular and intermolecular examples. Welding grade acetylene can even be used as the alkene substrate (eq 35). Imines can also be used as nucleophiles, and then a second nucleophile such as an allylstannane can react with the intermediate iminiumto yield dihydroisoquinolines (eq 36). ... 

Phase-transfer catalysts improve substantially the yields of the Reissert reactionFor example, isoquinoline, benzoyl chloride, and aqueous potassium cyanide, in the presence of benzyltriethylammonium chloride, give iV-benzoyl-1-cyano-l,2-dihydroisoquinoline in 82% yield (previous yield 38%). n.m.r. studies on the adducts of quinolines and isoquinolines with acetylene-dicarboxylates have necessitated revision of the structures of many of these adducts. For example, the so-called azepine adduct from 1-methyl-isoquinoline has been re-formulated as the cyclobutapyrrole (133). 

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