Purificación Cuadrado

The silyl-cupration and stannyl-cupration of allenes

Abstract The stoichiometric silyl-cupration of allene 7, followed directly by treating the intermediate cuprate with a proton, with a range of carbon electrophiles, and with chlorine gives the vinylsilanes 8–13. Alternatively, when iodine is the electrophile, the product is the vinyl iodide 16. This can then be metallated and treated with a proton or a range of carbon electrophiles to give the allylsilanes 18–21. More-substituted allenes also undergo silyl-cupration followed by protonation, phenylallenes giving vinylsilanes, and alkylallenes giving, on the whole, allylsilanes. Stoichiometric stannyl-cupration of allenes takes place, with similar but less reliable regiocontrol to that of the corresponding silyl-cupration.

Regiospecific synthesis of 5-silyl azoles

5-Silylisoxazoles bearing other silyl groups different to the more usual trimethylsilyl have been prepared by condensation of silylalkynones with hydroxylamine hydrochloride. The reaction with hydrazines is more complex and leads to 5-silylpyrazoles or the corresponding hydrazones, which can be cyclized by reaction with electrophiles. This has allowed us to synthesize 5-silylpyrazoles functionalized at C-4 by groups impossible to introduce by electrophilic substitution of the pyrazole nucleus.

The stannyl–cupration of acetylenes and the reaction of the intermediate cuprates with electrophiles as a synthesis of substituted vinylstannanes

Stannyl–cupration of acetylenes followed by electrophilic attack with a variety of electrophiles gives vinylstannanes.

Silyl-cupration of allene. A new route to silylated synthons

Abstract Silyl-cupration of allene followed by treatment with iodine anomalously gives the vinyl iodine 4 , a versatile synthetic intermediate.

Ring-formation from allyl- and vinylstannanes initiated by treatment with butyl-lithium

Abstract The allylstannane 1 and the vinylstannanes 3 , 5 and 7 cyclise when treated with butyl-lithium.

New findings on the regiochemistry of the silylcupration of allene

Abstract Allene 1 reacts at −40 °C with the phenyldimethylsilylcopper reagent 6 , with the opposite regioselectivity to that shown by the corresponding silylcuprate reagent 2 , to give allylsilanes 7 and 10 – 15 rather than vinylsilanes.

Synthesis of vinylsilanes by silyl-cupration of acetylenes using tert-butyldiphenylsilyl-cuprate reagents

The tert-butyldiphenylsilyl-cuprate 2 reacts with acetylenes 1 and 5–10 to give vinyl-cuprates 3 and 11, which react with electrophiles to give the vinylsilanes 4 and 12–17 carrying the relatively hindered and hence unreactive tert-butyldiphenylsilyl group. In comparative tests, the tert-butyldiphenylsilyl group shows some properties that are usefully different from those of relatively unhindered silyl groups and others that are similar.

Stannyl-cupration of acetylenes and the reaction of the intermediate cuprates with electrophiles as a synthesis of substituted vinylstannanes

Stannyl-cupration of acetylenes followed by electrophilic attack with a variety of electrophiles gives E-vinylstannanes. These can be used either to form acetylenes, thus achieving overall the addition of an ethynyl group, or to form carbon–carbon bonds in Stille reactions.

The reaction of tert-butyldiphenylsilylcuprates with allenes

Bis(tert-butyldiphenylsilyl)cuprate 1 reacts with allenes to form allyl- and vinyl-silanes. With allene itself the cuprate reagent shows a different regiochemistry from that of bis(phenyldimethylsilyl)cuprate. The regiochemistry can be controlled by choosing an appropriate reaction temperature. The intermediate cuprate 4 resulting from the addition of 1 to allene reacts with a wide variety of electrophiles giving functionalised allylsilanes. Phenylallenes isomerise to acetylenes.

t-Butyldiphenylsilyl-Lithium and Lithium Bis(t-Butyldiphenylsilyl)Cuprate. New Silylating Reagents

Abstract t-Butyldiphenylsilyl-lithium reacts with carbonyl derivatives to give α -hydroxysilanes in high yields. Lithium bis (t-butyldiphenylsilyl)cuprate reacts with α, β-unsaturated ketones and esters and with acyl chlorides to give β-silylcarbonyl1 compounds and acylsilanes. β-t-Butyldiphenylsilylketones are masked α, β-unsaturated ketones.