1- Allyl-3 indoles, cycloaddition

The intramolecular cycloaddition of nitrones derived from iV-allyl-2-indolecarbaldehyde was used to an entry to pyrrolo- and pyrido[ 1,2-a]indole skeletons . For instance, the cinnamyl-substituted aldehyde 157 upon treatment with benzylhydroxylamine affords to the nitrone 158, which upon heating in refluxing toluene leads to mainly the cycloadduct 159. 

C-C-C + N-N-N if). Several cases of intramolecular cycloadditions of azido groups to allyl ions and photochemi-cally generated zwitterions have been reported. Treatment of the indoles 255 and 257 with boron trifluoride etherate results in the formation of triazines 256 and 258 (Equations 112 and 113), and, after heterolysis, the cyclopentanol 259 furnishes the spiroanellated dihydro-1,2,3-triazine 260 (Equation 114) <1994JOG2682>. 

Nitrones generated from indole aldehydes readily undergo 1,3-dipolar cycloadditions to adjacent allyl double bonds. Pyrrolo[l,2-a]indoles are formed from l-allylindole-2-carbaldehydes (Scheme 137) <89TL1421,93AJC603>, whilst pyrrolo[3,2,1-i/lquinolines are obtained from l-allylindole-7-car-baldehydes (Scheme 138) <93AJC843>. 

The synthesis of l,2-cyclopropapyrrolo[l,2-a]indoles devised by Moody and Jones [54] was based on 1,3-dipolar addition of a diazo group to an alkene (Scheme 24). In this synthesis, indole-2-carboxaldehyde 169 was alkylated with allyl bromide in the presence of sodium hydride and then condensed with tosylhydrazine to give 170. The sodium salt of 170 underwent [3 + 2] cycloaddition, affording 171, when it was heated in benzene. Further heating in refluxing... 

A catalyst-free 4 + 3-cycloaddition of in tM-generated azoalkenes (134) with C,(V-cyclicazomethine imines (135) yielded highly functionalized 1,2,4,5-tetrazepine derivatives (136) in high yields (76-92%) under mild conditions (Scheme 40). " The Lewis-acid-promoted 4 + 3-cycloaddition reaction between the allylic cation of a heterocyclic alcohol with a furan or thiophene produced seven-membered ring-fused 5,7,6-tricyclic adducts with high regio- and stereo-selectivity. For the first time, the 2jt components are benzofuran-3-yl alcohols, benzothiophene-3-yl alcohols, and indole-3-yl alcohols. ... 

It is tempting to think that allylic cations would behave similarly to other stabilized cations in their reactions with alkyl azides. " In practice what happens is invariably an initial formal [3+3] cycloaddition of azide to the allylic cation, which is followed by a migration event (typically of hydride) or trapping by a nucleophile. Pearson and coworkers found that when sulfonylindole 27 was treated with SnCk at -78 °C, followed by basic workup, triazoline adducts 28 were obtained as mixture of chloride epimers (Scheme 7.24). When A -alkyl indoles (e.g. 29) were subjected to Lewis acidic conditions, tri-azines such as 30 were obtained as the sole products. In the former case involving an iV-sulfonyl indole, a [3+2] cycloaddition pathway explains the product, whereas the iV-alkyl indoles examined underwent [3+3] cycloaddition. 

Silylated diynes are used in the synthesis of methylene cyclopentanes, notably acyl derivatives of Oppoizer s camphor sultam, enediyne antibiotics, and CpCo omplexed dihydrocarbazoles, and ( )-Lysergene and (+)-LSD from a substituted indole and Me3SiC=CR through a [2+2+2]cycloaddition. Monosilylated hexatriyne and octatetrayne are used in the synthesis of the caryoynencin polyyne antibiotics, while triflate substituted disilyl polyynes result from the corresponding allyl derivative with The hydropyrolysis of bis-... 

The Ga(III)-catalysed three-component 4 -I- 3-cycloaddition reactions of indoles (128), ketones (129), and cyclohexadienes (130) produced cyclohepta[h]indole derivatives (131) in a single step at room temperature (Scheme 40). The 4-i-3-cycloaddition reactions of pyrroles with stabilized 2-(silyloxy)allyl cations formed tropinones in high yields (85%)4 The intramolecular 4-t-3-cycloaddition reaction of diaza-oxyallyl cationic intermediates and cyclic dienes yielded bicyclic ureas in good to excellent yields. ... 

EtAlCb catalyzes the Friedel-Crafts acylation of alkenes with acid chlorides, the formal [3 + 2] cycloaddition of alkenes with cyclopropane-1,1-dicarboxylates (eq 21), the Friedel-Crafts alkylation of anilines and indoles with ct-aminoacrylate esters, and the formation of allyl sulfoxides from sulfinyl chlorides and alkenes. EtAlCU induces the Beckmann rearrangement of oxime sulfonates. The cationic intermediates can be trapped with enol silyl ethers (eq 22). EtAlC is the preferred catalyst for addition of the cation derived from an a-chloro sulfide to an alkene to give a cation which undergoes a Friedel-Crafts alkylation (eq 23). ... 

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