Alkenes organomagnesiums

Sulfonylhydroxylamines and hydroxylamine O-sulfonic acid have found wide apph-cation in synthesis of amines from achiral or chiral organoboranes and boronate esters and the hydroboration-amination methodology is successfully used for direct amination of alkenes. 0-Sulfonyloximes were also found to be good reagents for synthesis of amines from organomagnesium, -copper and -zinc reagents. 

Uncatalyzed addition reactions of Grignard reagents with nonconjugated alkenes and aUcynes are of limited use in synthesis. However, carbon-carbon double bonds substituted by a leaving group, such as an acetate, are susceptible to be displaced by organomagnesium compounds presumably by an addition-elimination pathway. A few examples have been reported (equation 64). 

C-Alkylations have been performed with both support-bound carbon nucleophiles and support-bound carbon electrophiles. Benzyl, allyl, and aryl halides or triflates have generally been used as the carbon electrophiles. Suitable carbon nucleophiles are boranes, organozinc and organomagnesium compounds. C-Alkylations have also been accomplished by the addition of radicals to alkenes. Polystyrene can also be alkylated under harsh conditions, e.g. by Friedel-Crafts alkylation [11-16] in the presence of strong acids. This type of reaction is incompatible with most linkers and is generally only suitable for the preparation of functionalized supports. Few examples have been reported of the preparation of alkanes by C-C bond formation on solid phase, and general methodologies for such preparations are still scarce. 

The first alkyne cyclisations, from 377, 379 and 381, predate the early alkene cyclisations by a couple of years these three date from 1966173 and 1967,174 and illustrate the favourability of both exo and endo-dig cyclisation. All three generate benzylic vinyllithiums (378, 380 and 382), and both aryl (377, 379) and alkyl halides (381) are successful starting materials. Similar organomagnesium cyclisations were described at about the same time.175 However, it is not clear in these reactions how much of the product is due to participation of radicals in the mechanism - alkylbromides undergo halogen-metal exchange with alkyllithiums via radical intermediates (chapter 3).176 If it really is an anionic cyclisation, cyclisation to 378 is remarkable in being endo. Endo-dig anionic cyclisations are discussed below. 

Thirty years ago it was reported that reactions of Grignard reagents with 1-alkenes, catalysed by titanium tetrachloride, lead to organomagnesium compounds, formally derived by addition of HMgX to the carbon-carbon double bond [50,51], e.g. 

The nickel-catalysed reaction of organomagnesium compounds with dithioacetals, in which the initial substitution leads to elimination, giving a substituted alkene, is potentially useful [23, 24], as in the following procedure. Elimination of [3-alkoxy or alkylthio groups from the... 

Addition of an organomagnesium bond to an alkene, alkyne, or a benzenoid ring generates a new organomagnesium compound. With simple alkenes, addition occurs only under strenuous conditions. This reaction will be discussed later, with appropriate examples, as a reaction of organomagnesium compounds in the Section on Amides and Lactans.. 

Thiazol-2-yl allyl sulfides react with organomagnesium compounds in the presence of CuBr to afford optically active alkenes in good yields and selectivities <1996T10799>. Thiazole and benzothiazole allyl sulfides have been shown to react with excess ethyl diazoacetate in the presence of a copper(i) hexafluorophosphate acetonitrile complex to give, via formation of the resultant homoallylic sulfide intermediates, conjugated dienoic esters in good yields <1997TL3289>. /3-Ketosulfides of benzothiazole 143 are very prone to deprotonation by weak bases. Treatment... 

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