Alkenes reactions with dienes

Acyclic S-S dications 51 and 52 also give 1,2-disulfonium salts 90 in reactions with olefins.79 Formation of a mixture of diastereomers is observed in the case of 1,2-disubstituted alkenes. Reaction with conjugated dienes leads exclusively to the product of 1,4-addition 89 as mixtures of E- and Z-products whose ratio depends on steric factors (Scheme 34).79... 

The catalyzed reaction of acetylenic esters and alkenes can lead to ene products and/or cis [2 + 2]cycloaddition. The relative reactivity of alkenes established by reactions with dienes is 1,1-disubstituted > trisubstituted > monosubstituted and 1,2-disubstituted. Ene reactions predominate with alkenes containing two substi tuents on one carbon.1... 

The Pt(CH2 = CH2)(PPh3)2-catalyzed dehydrogenative double silylation of olefins and dienes with o-bis(dimethylsilyl)benzene was also examined by Tanaka and co-workers.61 The major product of the reaction with dienes, such as isoprene and penta-1,2-diene, is a result of 1,2-addition to the less substituted double bond. The reaction pathway for simple alkenes, shown in Eq. (19), appears to be dependent on the alkene substrate and, in some cases, on reaction temperature. Products resulting from 1,2-addition, 1, and 1,1-addition, 2, are detected for various substrates. In addition, hydrosilylation may occur to give the simple hydrosilylated product, 3, or a by-product, 4, derived from 1,4-migration of a methyl group in 3. 

Cyclopropane formation occurs from reactions between diazo compounds and alkenes, catalyzed by a wide variety of transition-metal compounds [7-9], that involve the addition of a carbene entity to a C-C double bond. This transformation is stereospecific and generally occurs with electron-rich alkenes, including substituted olefins, dienes, and vinyl ethers, but not a,(J-unsaturated carbonyl compounds or nitriles [23,24], Relative reactivities portray a highly electrophilic intermediate and an early transition state for cyclopropanation reactions [15,25], accounting in part for the relative difficulty in controlling selectivity. For intermolecular reactions, the formation of geometrical isomers, regioisomers from reactions with dienes, and enantiomers must all be taken into account. 

Ethyl 4.4,4-trifluorobut-2-ynoate reacts with various dienes (Table 3). " With a iionsymmctric diene, the cycloadduct is obtained as a mixture of regioisomers. This suggests that, unlike reactions with alkenes, reactions with alkynes arc not governed by the ester substituent. Cycloadducts can also undergo a further cycloaddition, in particular when the diene is used in excess. 

Azodicarboxylates are recognized for their ability to participate as 2ir components of HOMOdi e-con-trolled Diels-Alder reactions with dienes and for their participation in ene reactions with reactive al-kenes. 489 j, addition, electron-rich or reactive simple alkenes that do not contain a reactive allylic hydrogen atom have been shown to participate in competitive [2 + 2] and [4 + 2] cycloaddition reactions with azodicarboxylates in which the observed course of the reaction is dependent upon the solvent polarity and nucleophilic character of the alkene (Table 13). As may be anticipated, alkoxycarbonyl-aroyldiimides (4), diaroyldiimides (5), and aiylaroyldiimides (6) participate with increasing selectivity as 4tr components of [4 + 2] cycloaddition reactions. 

A simple one-pot synthesis of 2-chlorophosphinines (245) is afforded by the cycloaddition reactions with dienes of the phospha-alkene, ClP=CCl2, (generated by the action of triethylamine on dichloromethyldichlorophosphine). A route to... 

This compound was very unstable and decomposed within a few minutes at 0 . It could be trapped by cyclo-addition reactions with dienes. The alkene protons provided a sharp singlet at 6 4.93 in the H-n.m.r. spectrum, indicating a paratropic ring-current in the eight-membered ring. 

Titanocene-based complexes were also used in the hydrosilylation of a variety of alkenes and dienes (102,103). The reaction with dienes proceeds with an unprecedented regio- and diastereoselectivity to give ( -allylsilanes in good to excellent yields. The activation of the precatalyst in the excess of PhSiHa and in the absence of diene promotes the dehydrogenative double silylation of dienes to yield silacyclopentene according to (Scheme 16). 

Carbonyl-ene reactions of alkenes and glyoxylates were promoted effectively by Yb(OTf)3 [18]. With 20mol% of catalyst loading, desired homoallylic alcohols were obtained in good to high yield (Table 13.7). The reaction with diene gave the mixture of an ene product and a Diels-Alder product. Nakagawa et al reported imino ene reaction between alkenes and imines promoted by Yb(OTf)3-TMSCl (or... 

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