Enol silane propargylation

In 1993, Nicholas and his co-worker developed the stereospecific propargylic alkylation of chiral propargylic alcohols 30 with enol silanes 31 by using a stoichiometric amount of [Co2(CO)5L] (L = phosphite), but separation procedures of the produced diastereoisomers are necessary twice on the way to obtain the compounds specifically alkylated at the propargylic position 32 (Scheme 5). In 2001, Montana and his co-worker reported the diastereo-selective Nicholas alkylation of propargylic acetal complexes 33 bearing a chiral auxiliary with various enol silanes 34 (Equation (14)). A high diastereoselectivity is observed, but unfortunately, only low to moderate enantioselec-tivities are achieved in all cases. 

Scheme 27 Diastereoselective alkylation of propargyl alcohols with silyl enol ethers, allyl silanes and electron-rich arenes...

This reaction type is useful for the synthesis of tropane-like azabicycles (equations 94 and 95). Allyl-and propargyl-silanes are excellent nucleophiles in this process.Enone (125) is probably first transformed into an enol ether (c/. equation 70) before it cyclizes to the homotropane skeleton, which is eventually isolated as a mixture of enone (126) and chloride (127). 

Alkenes react in a similar fashion giving methoxymethyl derivatives, but in this case the intermediate carbenium ion is trapped with methoxide or another nucleophile such as a nitrile to afford the methyl ether or amide in a Ritter-like reaction (eq 11). In similar fashion, silyl enol ethers give ketones (eq 12), allyl-silanes afford homologated alkenes (eq 13), and stannylalkynes are converted to propargyl ethers. ... 

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