Alkyl hahde alkenes from

Because all the alkyl hahde formed from 1-pentene is the desired product, hut only half the alkyl halide formed from 2-pentene is the desired product, 1-pentene is the hest alkene to use for the synthesis. 

The clidnion derived from methyl d-nitraprapanodte is formed on treatment with LDA, and it is alkylated by alkyl hahdes exclusively at the 2-posidQn fEq 5 6 Eliminadonof HNOj v/ith DBU InTHF furnishes methyl ct-raethylenealkanoate fsee Secdon 7 3, which discusses alkene formadoni "... 

Because oxidative decarboxylation of carboxylic acids by lead tetraacetate depends on the reaction conditions, the co-reagents, and the structures of the acids, a variety of products such as acetate esters, alkanes, alkenes, and alkyl hahdes can be obtained. Mixed lead(IV) carboxylates are involved as intermediates as a result of their thermal or photolytic decomposition decarboxylation occurs and alkyl radicals are formed. Oxidation of alkyl radicals by lead(IV) species gives carbocations a variety of products is then obtained from the intermediate alkyl radicals and the carbocations. Decarboxylation of primary and secondary acids usually affords acetate esters as the main products (Scheme 13.41) [63]. 

If one carries out the substitution reaction with a solution of sodium hydroxide, the reaction stops being a substitution and an alkene is formed instead. Overall, HBr has been lost from the alkyl hahde, and the reaction is called an elimination (Scheme 2.15). 

A more efficient and more generahy applicable cobalt-catalysed Mizoroki-Heck-type reaction with aliphatic halides was elegantly developed by Oshima and coworkers. A catalytic system comprising C0CI2 (62), l,6-bis(diphenylphosphino)hexane (dpph 73)) and Mc3 SiCH2MgCl (74) allowed for intermolecular subshtution reactions of alkenes with primary, secondary and tertiary alkyl hahdes (Scheme 10.25) [51, 53]. The protocol was subsequently applied to a cobalt-catalysed synthesis of homocinnamyl alcohols starting from epoxides and styrene (2) [54]. 

When synthesizing an alkene using a Wittig reaction, the first thing you must do is decide which part of the alkene should come from the carbonyl compound and which part should come from the ylide. If both sets of carbonyl compound and yhde are available, the better choice is the set that requires the less sterically hindered alkyl haUde for the synthesis of the ylide via an Sn2 reaction. (Recall that the more stericaUy hindered the alkyl hahde, the less reactive it is in an Sn2 reaction see Section 9.1.)... 

Elimination of HBr from the reactant will form an alkene that can add water via an electrophilic addition reaction. The elimination reaction should he carried out und E2 conditions hecause the l iary alkyl hahde will undergo only elimination, so there will be no competing substitution product Hydroboration-oxidation will put the OH on the right carbon. Because R2BH will add preferentially to the less sterically hind ed side of the double bond and the ovarall hydroboration-oxidation reaction results in the syn addition of water, the target molecule (as well as its enantiomer) is obtained. 

The dehydrohalogenation of an alkyl hahde is a good laboratory method for the synthesis of alkenes because alkyl hahdes are readily available from reactions of several other starting materials. Considered by itself, this reaction has a very unfavorable eqmhbrium constant. However, if we use a strong base such as alkoxide anion to extract a proton on the carbon adjacent to the bromine, the reaction becomes highly favorable. 

Our aim in this chapter is to present the most important advances in the domino reactions of carbohydrates based on the metal-promoted ring opening of cyclic sugars. These procedures, promoted by different low-valent organometaUic reagents, start with the addition of the metal to an electrophihc site (i.e., an alkyl hahde, a carbonyl, an alkene, or an alkyne), followed by reductive ehmination to the open-chain sugar. From this open-chain sugar intermediate, the next reaction takes place under the same reaction conditions. 

The carbopalladation of a triple bond is faster than that of a double bond, even when the alkene is tethered to the initially formed arylpalladium halides. This is exemphfled by the formation of a tetracychc system from o-isobutenyliodobenzene and diphenylethyne. This process is also terminated by ortho attack of the intermediate neopentyl-type alkyl-paUadium hahde on one of the arene rings (Scheme... 

In Chapter 9, we saw that we can prepare alkenes by dehydrohalogenation. The dehydration of alcohols also gives alkenes, but this reaction occurs with rearrangement of the carbocation, and gives mixtures of products having different carbon skeletons. The elimination of a hydrogen hahde from an alkyl halide is a complex process. We must consider both rcgiochemistry and stereoelectronic effects. These effects are related to the mechanism of the reaction, which may be either E2 or El. 

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