Addition to Alkynes and Alkenes

Intramolecular Addition to Alkenes and Alkynes. Organolithium reagents can react with alkenes or alkynes in an intramolecular reaction, although both are relatively inert to the analogous intermolecular reaction. Ward treated alkynyl bromide 263 with n-butyllithium and observed a 60% yield of 

A solution of nm/-4-hydroxy-3-methyltridec-l-ene (850 mg, 4.0 mmol) in ether (20 ml) is cooled to 0° as ethylmagnesium chloride (1 m, 20 ml, 20 mmol) is added dropwise by syringe. The mixture is allowed to warm to 20° and dicyclopentadienylzirconium dichloride (58.4 mg, 0.2 mmol) is added. The mixture is stirred at about 25° for 12 h. 

A subsequent reaction with trimethyl borate followed by hydrogen peroxide (see Section 15.1) gave the alcohol (1) (72%), with over 95% with the relative stereochemistry shown [16]. 

Copper(i) catalysis of the addition of organomagnesium compounds to alkynes has been observed, but stoichiometric organocopper reagents, derived from organomagnesium compounds, are more effective in the absence of other activating features [4]. 

There are three important exceptions to the generalization which opens this chapter (a) intramolecular additions, (b) additions to alkenes and alkynes bearing n-donor substituents able to provide anchimeric assistance, and (c) addition of allymagnesium derivatives. These beneficial features may operate alone or together. 

Intermolecular reactions of this type suffer from variable yields and regio-and/or stereoselectivity, though they can give good results in favourable cases. Some examples have been noted in paragraph (b), above, and another is shown in the following equation [33]  

---

For a summary and detailed discussion of the stereochemistry of electrophilic additions to alkenes and alkynes see R. C. Fahey, in Topics in Stereochemistry, Vol. 3,... 

R =H, R =alkyl for terminal alkynes R =alkyl, R =H for terminal alkenes Catalytic Cycle for Addition to Alkenes and Alkynes... 

Silylstannanes undergo regiospecific addition to alkenes and alkynes with scission of the Sn—Si bond, as illustrated in reactions 15 and 16272. 

In addition to alkenes and alkynes, allenes have attracted considerable interest due to their unique reactivity and multireaction sites. Therefore, transition-metal-catalyzed nucleophilic addition reaction of amines and imines to allenes has been extensively studied to prepare biologically important amines and nitrogen-heterocycles.31,31d... 

Gattermann aldehyde synthesis, 9, 2 Gattermann-Koch reaction, 5, 6 Germanes, addition to alkenes and alkynes, 13, 4 Glycals,... 

The versatility of these [4+2] heterocyclization reactions is a consequence of the wide range of ene and diene components which can be used. In addition to alkenes and alkynes functioning as ene components, a variety of heterodienophiles is available such as electron-deficient imines (e.g. equation 89), nitriles e.g. equation 90), electrophilic carbonyl compounds (e.g. equation 91), thiocarbonyl compounds (e.g. equation 92), singlet oxygen (e.g. equation 93), nitroso compounds (e.g. equation 94), sulfenylsulfonamides (e.g. equation 95) and azo compounds (e.g. equation 96). Many of these reactions proceed with excellent regioselectivity and stereoselectivity, probably because in many instances they involve... 

Addition reactions occur in compounds having n electrons in carbon-carbon double (alkenes) or triple bonds (alkynes) or carbon-oxygen double bonds (aldehydes and ketones). Addition reactions are of two types electrophilic addition to alkenes and alkynes, and nucleophilic addition to aldehydes and ketones. In an addition reaction, the product contains all of the elements of the two reacting species. 

Several of the synthetic methods appropriate to these compounds have already been described as applicable to small rings (cyclization by metalloid hydride addition to alkenes and alkynes, and coupling through metal halide elimination). While much of the chemistry of these compounds is similar to that of acyclic derivatives, a few peculiarities are worthy... 

Although HI addition to alkenes and alkynes is faster than that of the other hydrohalides and free radical anti-Maikovnikov additions are not a problem, this reaction has received less attention than the others.173 The hydroiodination of alkenes is most commonly run using concentrated HI in water or acetic acid at or below room temperature. While the early literature suggests that simple terminal alkenes afford small amounts of anti-Markovnikov products, only Markovnikov products have been reported in the more recent literature (equations 125-129).67 176-179... 

Another approach in the study of the mechanism and synthetic applications of bromination of alkenes and alkynes involves the use of crystalline bromine-amine complexes such as pyridine hydrobromide perbromide (PyHBts), pyridine dibromide (PyBn), and tetrabutylammonium tribromide (BiMNBn) which show stereochemical differences and improved selectivities for addition to alkenes and alkynes compared to Bn itself.81 The improved selectivity of bromination by PyHBn forms the basis for a synthetically useful procedure for selective monoprotection of the higher alkylated double bond in dienes by bromination (Scheme 42).80 The less-alkylated double bonds in dienes can be selectively monoprotected by tetrabromination followed by monodeprotection at the higher alkylated double bond by controlled-potential electrolysis (the reduction potential of vicinal dibromides is shifted to more anodic values with increasing alkylation Scheme 42).80 The question of which diastereotopic face in chiral allylic alcohols reacts with bromine has been probed by Midland and Halterman as part of a stereoselective synthesis of bromo epoxides (Scheme 43).82... 

---