Carbon intramolecular

Under ordinary conditions, reduction of these imines in dimethylformamide is a two-electron process involving saturation of the carbon-nitrogen double bond [181] because the radical from protonation of the radical-anion is more easily reduced than the starting imine. Immonium salts with two or more phenyl substituents are reduced reversibly in acetonitrile to the radical-zwitterion such as 42. Other immo-niura salts, e.g. 43, are reduced irreversibly to the dimer [182]. Radical-zwitterion intermediates generated from immonium salts exhibit nucleophilic character on carbon. Intramolecular interaction between the reduced immonium function and a... 

In the latter example, cyclization occurs exclusively to the carbonyl carbon rather than with nucleophilic displacement of chloride at the a-carbon. Intramolecular alkylation of nitrogen does occur in other systems the 3-chloropropylsulfonylhydrazide (194), for example, ring closes to give the 1,2,3-thiadiazine dioxide (195) on treatment with base (62JPR(19)56). 

In this manner, a hydroformylation/condensation sequence of 0-vinyl-anilines give indoles directly. The starting o-vinylanilines are obtained by Heck reaction of the corresponding o-haloanilines. Hydroformylation of these styrene-type olefins proceeds preferably at the benzyl carbon. Intramolecular condensation gives pharmacologically interesting tryptophols and tryptamines in mediocre to good yields (Scheme 12, Table 1) [47]. 

If a radical is joined to a double bond by a chain of three or more carbons, intramolecular addition generates a ring. The regioselectivity of such additions is governed more by stereoelectronic factors than by substituents on the double bond. Thus, five-membered ring formation byway of a l°-cyclized radical dominates the products, as shown in Scheme 2.47. 

Heck reactions involving nonaromatic components are particularly versatile synthetic processes. For example, 1,2,4-trienes and l,2-dien-4-ynes are readily prepared from propargyl carbonates." Intramolecular Heck cyclization followed by Diels-Alder or nucleophilic attackleads to bicyclic products. Substituted pyrrolidines and piperidines are formed by coupling of alkenyl sulfonamides with vinylic halides. ... 

Secondary alkyl chloride with good nucleophile (Et2N) can participate in the formation of an aziridinium intermediate that is attacked by HO in Sj 2 mode to give an amino-alcohol (Scheme 2.42). The CH2 carbon has less steric crowing than the CHMe carbon. Intramolecular reactions, including participation, that give three-, five-, or six-membered rings are usually faster than intermolecular reactions. 

For instance, when refluxing L93 (R = NO2, Ri = n-CsHy) in DMF in the presence of potassium carbonate, intramolecular cyclisation takes place with the isolation of L94. This exists in solution in tautomeric forms L94a and L94b (Eq. 2.57) [132]. 

The third chapter is devoted to the all-carbon intramolecular Alder ene reaction. The tables in that chapter summarize all examples that could be found in the literature through 1981, with several additional examples from 1982. Leading references to heterocyclic ene reactions are also included in this chapter. 

Intermolecular addition of terminal alkynes to alkynoates has resulted in some unusual regioselectivity, up to exclusive formation of the G-G bond at the a-carbon." Intramolecular dimerization of a sterically constrained trialkyne proceeding through alkynylpalladium(ii) and yn-enylpalladium(ii) was reported." Interestingly, one of the tolyl groups of the ancillary phosphine ligand was transferred to the remaining alkynyl moiety. 

Table 5 Carbon-carbon intramolecular through space contact distance, (A), between overlapping carbons (see text for definition) and smallest contact distances for each molecule...

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