1- Acyl-2-vinylcyclopropanes

Cuprous methyltrialkylborates (54), which are prepared from trialkylboranes, methyl lithium and cuprous halide, are useful alkylating agents. Reaction with acrylonitrile for example gave the corresponding 1,4-adducts which are converted into alkyl cyanides by hydrolysis (Scheme 6). Yields are generally excellent, provided cuprous bromide is used and not the chloride or iodide. The complex (54) also reacts readily with 1-acyl-2-vinylcyclopropane to form 1,6-adducts which are hydrolysed to the corresponding /raws -y.S-unsaturated ketone (55) in good yield. 

The oxygen-induced 1,6-addition of trialkylboranes with 1-acyl-2-vinylcyclopropanes occurs but the yields are quite low. 

Mild Ni(0)-catalysed rearrangements of l-acyl-2-vinylcyclopropanes to substituted dihydrofurans have been developed.86 The room temperature isomerizations afford dihydrofuran products in high yield. A highly substituted, stereochemically defined cyclopropane has been employed in the rearrangement to evaluate the reaction mechanism. The Cu(II)-catalysed cycloisomerization of tertiary 5-en-l-yn-3-ols with a 1,2-alkyl shift affords stereoselectively tri- and tetra-cyclic compounds of high molecular complexity (Scheme 29).87 A proposed mechanism has been outlined in which... 

Using a somewhat similar reaction sequence cw-l-bromo-2-vinylcyclopropane was reacted with various acid chlorides and transformed stereospecifically to 1-acyl-2-vinylcyclopro-panes. Very good yields were obtained thus, when the bromide was allowed to react successively with tert-butyllithium, phenylsulfanylcopper and cyclobutanecarbonyl chloride at — 78 °C, cyclobutyl d5-2-vinylcyclopropyl ketone (2a) was isolated in 93% yield. 

Trialkylboranes are able to transfer an alkyl group onto l-acyl-2-vinylcyclopropanes with simultaneous opening of the ring. Since this reaction requires oxygen, a radical mechanism has been postulated. The yields of these reactions were too low for practical purposes however, this difficulty was overcome by the use of lithium dialkylcuprates rather than trialkylboranes as alkylating agents or by the use of copper(I) methyltrialkylborates, The reaction... 

Carbosily lotion. 1.3-Dici 47-95%) on reaction with acyl chlonr Decarbonylation of the acyl chloride Vinylcyclopropanes. A high... 

Iron carbonyl complexes are obtained by irradiation of iron pentacarbonyl with vinylcyclopropanes. The principal modes of reaction are (i) metal insertion into a strained bond with hydrogen migration to give diene-Fe(CO)3 complexes, (ii) metal carbonyl insertion to give a n-allyl-complexed acyl iron tricarbonyl, and (iii) cycloinsertion of CO across the homodiene to give a cyclohexenone. Similar types of... 

C-C cleavage of strained rings and ketones has been used to develop useful catalytic reactions. For example, vinylcyclopropanes and vinylcyclobutanes react with alkynes (Equation 6.66) to generate products from 5+2 and 6+2 addition processes that form seven- and eight-membered ring products by overall transformations that are homologs of the Diels-Alder reaction. " The mechanism of these catalytic reactions continues to be studied, but these reactions most likely occur by coordination of the olefin to rhodium and insertion of the metal into the cyclopropene or cyclobutane. Decarbonylation of dialkyl ketones, including relatively unstrained cyclic ketones, has been reported and most likely occurs by oxidative addition into the acyl-alkyl C-C bond, subsequent de-insertion of CO, and C-C reductive elimination. 

Scheme 2.58 Ni(0)-catalyzed rearrangement of l-acyl-2-vinylcyclopropane 73. Table 2.2 Ring-opening functionalizations of donor-acceptor cyclopropanes.

It has been suggested that the recently observed 1,4-addition of trimethylsilyl-lithium to a/S-unsaturated ketones and the 1,4-addition of cuprous methyl-trialkylborates to l-acyl-2-vinylcyclopropanes also occur by a one-electron-transfer mechanism the latter reaction provides a useful synthetic route to (E)-a -unsaturated ketones. 

A very versatile polymeric scaffold for site-specific double PPM is poly( 1 -aceto-l-pentalluorophenoxycarbonyl-2-vinylcyclopropane) [poly(APVCP)] (see Scheme 8) [139]. In this case, the two-step modification is performed in a sequential batch process. Following aminolysis by treatment with various primary amines, the ketone can be converted in the presence of hydrazide or hydroxylamine derivatives. Fmthermore, the ketone can be reduced to the secondary alcohol, which is subsequently converted into the ester or carbamate through the use of different acyl halides and isocyanates. 

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