Vinylsilanes with imines

Silyl-2-pyrazolines are obtained in moderate to excellent yields by the [2 + 3] cycloaddition of a vinylsilane with diphenylnitrile imine.120... 

Beyond palladium, it has recently been shown that isoelectronic metal complexes based on nickel and platinum are active catalysts for diyne reductive cyclization. While the stoichiometric reaction of nickel(O) complexes with non-conjugated diynes represents a robust area of research,8 only one example of nickel-catalyzed diyne reductive cyclization, which involves the hydrosilylative cyclization of 1,7-diynes to afford 1,2-dialkylidenecyclohexanes appears in the literature.7 The reductive cyclization of unsubstituted 1,7-diyne 53a illustrates the ability of this catalyst system to deliver cyclic Z-vinylsilanes in good yield with excellent control of alkene geometry. Cationic platinum catalysts, generated in situ from (phen)Pt(Me)2 and B(C6F5)3, are also excellent catalysts for highly Z-selective reductive cyclization of 1,6-diynes, as demonstrated by the cyclization of 1,6-diyne 54a.72 The related platinum bis(imine) complex [PhN=C(Me)C(Me)N=Ph]2Pt(Me)2 also catalyzes diyne hydrosilylation-cyclization (Scheme 35).72a... 

The coupling reactions of imines with vinylsilanes serve as a key protocol for the synthesis of various alkaloids (equation 61 and 62)129-132. 

A final approach to the c -3a-arylhydroindole skeleton that has resulted in a concise total synthesis of ( )-epielwesine (449) featured the acid-promoted cyclization of (Z)-vinylsilane imines such as 575 (Scheme 53) (2/9). Thus, sequential alkylation of 3,4-(methylenedioxyphenyl)acetonitrile (432) with (Z)-4-bromo-l-butenyltrimethylsilane and l-bromo-2-chloroethane provided... 

Coverage in this chapter is restricted to the use of alkenes or alkynes as enophiles (equation 1 X = Y = C) and to the use of ene components in which a hydrogen is transferred. Coverage in Sections 1.2 and 1.3 is restricted to ene components in which all three heavy atoms are carbon (equation 1 Z = C). Thermal intramolecular ene reactions of enols (equation 1 Z = O) with unactivated alkenes are presented in Section 1.4. Metallo-ene reactions are covered in the following chapter. Use of carbonyl compounds as enophiles, which can be considered as a subset of the Prins reaction, is covered in depth in Volume 2, Chtqiter 2.1. Addition of enophiles to vinylsilanes and allylsilanes is covered in Volume 2, Chapter 2.2, while addition of enophiles to enol ethers is covered in Volume 2, Chapters 2.3-2.S. Addition of imines and iminium compounds to alkenes is presented in Volume 2, Part 4. Use of alkenes, aldehydes and acetals as initiators for polyene cyclizations is covered in Volume 3, Chapter 1.9. Coverage of singlet oxygen, azo, nitroso, S=N, S=0, Se=N or Se=0 enophiles are excluded since these reactions do not result in the formation of a carbon-carbon bond. 

The ene and Prins reactions are not mechanistically distinct. Coverage will therefore be organized by the nature of the carbonyl compound, with intermolecular reactions presented first, followed by intramolecular reactions. The emphasis will be on material published since the field has been reviewed " and on examples demonstrating the stereo-, regio- and chemo-selectivity of these reactions. Coverage is restricted to the addition of carbonyl and thiocarbonyl compounds to simple alkenes. Addition of carbonyl compounds to vinylsilanes, allylsilanes and enol ethers is covered in the following chapters. Addition of imines and iminium compounds to alkenes is presented in Part 4 of this volume. Ene reactions with alkenes and alkynes as enophiles are covered in Volume 5, Chapter 1.1. Use of aldehydes and acetals as initiators for polyene cyclizations is covered in Volume 3, Chapter 1.6. 

The hydroarylation of styrenes is a very useful transformation. Genet and coworkers [70a] were the first to report the Ru-cat2dyzed hydroarylation of styrenes. This group later reported the successful hydroarylation of aromatic ketones and imines with both vinylsilanes and styrenes [70b]. See Figure 4.38 for the Co-cat2dyzed transformation. 

The organolithium reagent (1) also reacts with a wide variety of other electrophiles, including silyl chlorides to provide bis(silyl)methane derivatives, and nitriles to provide -sUyl amines after in situ reduction of the intermediate imine derivative. a-Silyl epoxides are opened to provide the substituted vinylsilane. Reaction of (1) with arenesulfonyl fluorides provides a-silyl sulfones, key intermediates for the preparation of vinyl sulfones. Reaction of the lithium reagent (1) with alu-... 

The Imhof group demonstrated a three-component coupling reaction of a, -unsaturated imines with CO and alkenes catalyzed by Ru3(CO)j 2, which produced a,a-disubstituted, y-unsaturated y-butyrolactams [62]. Similar reactions were also independently explored by Chatani and coworkers (Eq. (7.53)) [63]. Ethylene, vinylsilane, and norbornene could be used as the alkene partners, but the terminal alkenes were not compatible with the reaction system. The imine substrates bearing electron-withdrawing group showed low reactivity. 

---