Silylformylations regioselectivity

Intramolecular cyclization is particularly effective to terminal alkynes containing three or four methylene units between acetylenic and silyl moieties such as 158, 160, and 162. But-3-ynylmethylphenylsilane does not give any positive result for CO incorporation. Regioselectivity for the silylformylation is completely reversed from the one in the standard silylformylation discussed in Section 11.14.2.2. A bulky /ft7-butyl group in 162 (R = Bu ) plays an... 

Although the regioselectivity for the silylformylation of 1-alkynes is excellent, that of internal alkynes is low except for 2-alkynoates (vide supra). Also, in the reactions of 1-alkynes, the silyl group is always delivered to the terminal position and the formyl to the C-2 position, thus it is impossible to synthesize 3-silyl-2-alkenals, which requires opposite regioselectivity. Intramolecular directed reactions can circumvent these limitations and expand the scope of the silylformylation of alkynes. 

Silylformylation of alkynes.1 0-Silyl-a,0-enals can be prepared by reaction of dimethylphenylsilane and carbon monoxide with alkynes catalyzed by Rh4(CO)12. Yields are improved if triethylamine is also present. Regioselectivity in the reaction with internal alkynes is controlled by steric factors. 

With excellent chemo- and regioselectivity, alkynes and especially terminal alkynes 49 undergo silylformylations (Scheme 7) [21]. Instead of hydrogen, phenyldimethylsilane is used, which adds, after activation of the Si-H bond by the metal catalyst, exclusively via the silicon-metal and not via the hydrogen-metal bond onto the al-... 

SUylation. Hydrosilylation of 1-alkynes in the presence of a Rh(I) catalyst is regioselective. A reversal of the stereoselectivity is possible by adding PhjP and changing the solvent.Silylformylation is conducted at 1 atm. CO at 0°C. ... 

The silylformylation of 1-alkynes has been studied extensively affording (Z)-l-silyl-2-formyl-l-alkenes high regioselectivity. However, internal alkynes have not demonstrated high regioselectivity. Biffis et al. have reported using a cationic dirhodium(II) complex to achieve improved chemoselectivity for the silylformylation of internal alkynes.In addition, intramolecular silylformylation reactions were developed to aid in the regioselectivity of silylformylation of internal alkynes. ... 

The regioselectivity in the silylformylation of terminal and internal acetylenes seems to be governed in general by the steric bulkiness of the substituents. Thus the bulky silyl group goes to the least hindered carbon, and consequently the formyl group is introduced into the most substituted one [137]. The electronic effect is the major factor that determines the regiochemistry of propiolate derivatives. Hydrosilylation is a competitive reaction. 

To also add an application to aromatic compounds we cite the Heck-hydroformylation sequence [57] (see 121) and to extend these directed additions into the silicon and boron field a regioselective silylformylation-allyl silylation sequence [58] and a hydroformylation-allyl boration hydroformylation cascade are included. 

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