Silane-terminated intramolecular

As an application of this methodology to the syntheses of natural products, Sannicolo et al. have reported the preparation of benzazepine and tetra-hydroisoquinoline derivatives by silane-terminated intramolecular Heck reactions. These workers argued that one main disadvantage of the Heck reaction... 

The general procedure for a silane-terminated intramolecular enantioselective Heck reaction is exemplified by Scheme 3-60 [61a,b, 259]. A mixture of [Pd2(dba)3 - CHCI3] (0.025 mmol,... 

Scheme 3-5 Silane-terminated intramolecular Heck reaction [61].

Tietze, L.E. and Schimpf, R. (1994) Regio- and enantioselective silane-terminated intramolecular Heck reactions. Angew. Chem., Int. Ed. Engl., 33,1089-91. 

Tietze, L.R and Modi, A. (2000) Regioselective silane-terminated intramolecular Heck reaction with alkenyl trillates and alkenyl iodides. Eur. J. Org. Chem., 1959-64. 

Scheme 7.4 Syntheses of benzazepines and tetrahydroisoquinolines by intramolecular silane-terminated Heck reactions with (T )-BITIANP and ( + )-TMBTP ligands.

Clive and coworkers have developed a new domino radical cyclization, by making use of a silicon radical as an intermediate to prepare silicon-containing bicyclic or polycyclic compounds such as 3-271 and 3-272 (Scheme 3.69) [109], After formation of the first radical 3-267 from 3-266, a 5-exo-dig cyclization takes place followed by an intramolecular 1,5-transfer of hydrogen from silicon to carbon, providing a silicon-centered radical 3-269 via 3-268. Once formed, this has the option to undergo another cyclization to afford the radical 3-270, which can yield a stable product either by a reductive interception with the present organotin hydride species to obtain compounds of type 3-271. On the other hand, when the terminal alkyne carries a trimethylstannyl group, expulsion of a trimethylstannyl radical takes place to afford vinyl silanes such as 3-272. 

It is difficult to find crosslinking systems that are ideal in that all functional groups are of equal reactivity and intramolecular cyclization is negligible. The crosslinking of vinyl terminated poly(dimethylsiloxane) polymers with tri- and tetrafunctional silanes appears to be an exception. Thus the calculated and experimental pc values were 0.578 and 0.583, respectively, for the tetrafunctional silane and 0.708 and 0.703, respectively, for the trifunctional silane (with r — 0.999) [Valles and Macosko, 1979]. 

The (dienyl)iron cations of type (248) and (265) are susceptible to reaction with nucleophiles. For the (cyclohexadienyl)iron cations, nucleophilic attack always occurs at a terminal carbon, on the face of the ligand opposite to the metal, to afford / -cyclohexadiene products. Typical nucleophiles used are malonate anions, amines, electron-rich aromatics, silyl ketene acetals, enamines, hydrides, and aUyl silanes intramolecular nucleophilic addition is also possible. The addition of highly basic organometaUic nucleophiles (Grignard reagents, organolithiums) is often problematic this may be overcome by replacing one of the iron carbonyl... 

In the presence of an electrophilic catalyst like PtCl2, terminal alkyne 23 containing an allylic silane functionality undergoes exo-carbocydization to give 24 possibly through intramolecular trapping of a Pt(II)-coordinated triple bond or a vinyl cation intermediate with the allylic silane moiety (Scheme 5.6) [13]. Pd(II), Ru(II), and Ag(I) salts also serve as a catalyst of this cydization. 

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