Ketone, cyclopropylmethyl

Vapor phase thermolysis of 2,5-hexadien-l-ols at 260°C affords cyclopropylmethyl ketones . The reaction has been proposed to proceed via homodienyl migration of hydrogen and is stereospecific (equation 118). l-(l-Alkynyl)-2-vinyloxiranes undergo successive Cope rearrangements at 300-350°C to give 2-(l-alkynyl)cyclopropane-carbaldehydes (equation 119) . Acid-catalyzed intramolecular acetalization followed by... 

Vapor-phase thermolysis of hexa-2,5-dien-l-ols 5 at 260 °C afforded cyclopropylmethyl ketones 6. The reaction was stereospecific and has been proposed as proceeding via oxy-homodienyl migration of hydrogen. 

Conversion of Cyclopropyl Ketones and Cyclopropylmethyl Ketones to Cyclopropylvinyl Derivatives... 

Various alkyl cyclopropylmethyl ketones and cyclopropylacetaldehydes have been converted to 2-cyclopropylalk-l-enyl derivatives, including acetates,chlorides,tri-... 

Tosylhydrazones of alkyl cyclopropylmethyl ketones were converted to alkenylcyclo-propanes on treatment with a strong base. For example, treatment of 3... 

Three types of products have been observed in intermolecular acylations of homoallylic silanes, the major one being cyclopropylmethyl ketones, along with minor amounts of 3-butenyl ketones and -chlo-ro ketones. It is likely that all derive from the carbenium ion formed by acylation of the double bond, which then undergoes cyclodesilylation or hydride transfer followed by 3-elimination (Scheme 14). The former leads to the cyclopropane, which can ring open to give the chloro products. The latter pathway gives the butenyl ketone, and is supported by location of substituent positions on methylated substrates. However, the direct acylation of the carbon-silicon bond should not necessarily be excluded in consideration of more general cases. Titanium tetrachloride seems the preferred catalyst in these cyclodesilyl-ations, and low temperatures minimize the formation of the chloro by-products. Intramolecular versions... 

C—C Bond Formation using Organosilanes. Under catalysis by TiCU, allylsilanes transfer the allyl group, with rearrangement, to ketones, a/3-unsaturated ketones (conjugate addition), and quinones (initially giving the carbonyl addition product which then further rearranges to the 2-allyl-l,4-hydroquinone). But-3-enyl-silanes react with acid chlorides to yield cyclopropylmethyl ketones [reaction (3)) under similar conditions. 

The biradical benzo-l,2 4,5-bis(l,3,2-dithiazolyl) (BBDTA) is known in the literature but characterization is incomplete. A new study reports the electronic, molecular, and solid-state structure of BBDTA.224 The lifetime of an alkyl phenylglyoxalate-derived 1,4-biradical has been estimated, using the cyclopropylmethyl radical clock , to be in the range 35—40 ns.225 The indanols (88) and their C(3) methyl and trideuteromethyl analogues have been prepared from phenyl benzyl ketone via photo-cyclization of an intermediate 1,5-biradical species.226,227 Selectivity for these products over their C(l) epimers is high but is profoundly effected by substitution in the benzyl ring or the alkyl side-chain. The findings are rationalized in terms of the conformational preference of the intermediate 1,5-biradicals. 

MISCELLANEOUS REACTIONS OF DIHYDROPYRIDINES Additional tests for net hydride transfers initiated by single-electron transfer include the use of substrates in which such pathways would necessarily involve readily ring-opened cyclopropylmethyl or readily cyclized 5-hexenyl radicals. Products from these radical reactions are not formed in NAD+/ NADH dependent enzymic reductions or oxidations (Maclnnes et al., 1982, 1983 Laurie et al., 1986 Chung and Park, 1982). Such tests have also been applied in non-enzymic reductions. Thus cyclopropane rings in cyclopropyl 2-pyridyl ketones, or imines of formylcyclopropane (van Niel and Pandit, 1983, 1985 Meijer et al., 1984) survive Mg+2 catalysed reduction by BNAH or Hantzsch esters but are opened by treatment with tributylin hydride. 

Ester, nitrile, or ketone functions are tolerated in the method. Aryl chlorides can be applied with only slightly decreased yields. For 3-bromopropionate the bipyridine ligand was mandatory for the success of the reaction. The involvement of radicals is supported by ring opening occurring when cyclopropylmethyl bromide was used as the substrate (cf. Part 1, Fig. 8). 

In a more recent study Co(dppe)I2 was used as a catalyst for reductive additions of primary, secondary, and tertiary alkyl bromides or iodides 249 to alkyl acrylates, acrylonitrile, methyl vinyl ketone, or vinylsulfone 248 in an acetonitrile/water mixture using zinc as a stoichiometric reducing agent [305]. The yields of the resulting esters 252 were mostly good. The authors tested radical probes, such as cyclopropylmethyl bromide or 6-bromo-1-hexene (cf. Part 1, Fig. 8). However, the latter did not cyclize, but isomerized during addition, while the former afforded complicated mixtures. On this basis the authors proposed a traditional two-electron mechanism to be operative the results do not, however, exclude a radical-based Co(I) catalytic cycle convincingly (Fig. 61). 

S-CHR — Li/Keton] Thiobutansaure 3,3-Dimethyl-2-oxo- -tert.-butylamid E5, 1241 (Keton/SOCl2 Amin) Thiocarbamidsaure N-Cyclopropylmethyl-N-propyl- -S-ethylester E4, 296 (Cl - ... 

Cyclopropyl ketone 222 (Scheme 55) was prepared to probe the mechanism of the cleavage reaction [39,40]. Isolation of 224 where the cyclopropyl ring is intact (Scheme 56) suggests cleavage proceeds via formation of radical 227 rather than ketyl radical anion 226, formed by single-electron transfer to the ketone carbonyl, as cyclopropylmethyl radical anions are known to undergo facile fragmentation. 

The hydrostannation of carbonyl compounds to give alkoxystannanes (equation 14-5) can follow a homolytic or heterolytic mechanism depending on the structure of the reactants and on the reaction conditions (Section 20.1.3). This existence of alternative mechanisms is elegantly demonstrated in the reduction of cyclopropyl methyl ketone by tributyltin hydride. In methanol, 1-cyclopropylethanol is formed in a polar process, but, with irradiation with UV light, the main product is pentan-2-one, which is formed by ring opening of the cyclopropylmethyl radical by P-scission (Scheme 14-1)14... 

Several cyclopropylmethyl cations have been prepared by treating cyclopropyl ketones with super acids at low temperature. The hydrogen fluoride/antimony(V) fluoride mixture has been most frequently employed, but hydrogen chloride in antimony(V) chloride and antimony(V) fluoride/fluorosulfuric acid/fluorosulfuric chloride have also been used. The counterion is, therefore, hexahaloantimonate. Yields were generally not reported an exception was the isolation of tricyclopropylmethylium hexafluoroantimonate in 86% yield on reaction of tricyclopropylmethanol with antimony(V) fluoride. " ... 

Manganese oxides are well-established oxidizing agents, which have been used for the conversion of cyclopropylmethyl alcohols to the corresponding carbonyl compounds. Activated manganese dioxide in an inert solvent has been employed to prepare aldehydes - as well as ketones,e.g. oxida-... 

A number of intermediates related to the cyclopropylmethyl radical undergo rapid ring opening. 1-Cyclopropylvinyl radicals 35 rearrange to 2-(allenyl)ethyl radicals 36, while radical anions 37, formed by one-electron reduction of cyclopropyl ketones, ring open to give enolate radicals... 

Diradicals, including 1,3- and 1,4-types incorporating the cyclopropylmethyl unit 39 and 40, have been generated from ketones, cyclic diazenes, and in various other ways (see Section 2.4.1.5.2.7.). The intra- and intermolecular reactions of the 2-(spiro[2.5]octadien-6-yl)ethyl diradical 41 lead to some novel products. ... 

Organotin radicals, and some related species, add to the carbonyl oxygen of cyclopropyl ketones 1 to produce a,a-disubstituted cyclopropylmethyl radicals. j -Scission, followed by hydrogen transfer with the organotin hydride, yields a mixture of enolates and isomeric a-stannyl ketones. Although the enolates can be isolated, they are usually hydrolyzed in situ with methanol to give the corresponding ketones 3. 

A reagent consisting of samarium(II) iodide and 1,3-dimethyl-3,4,5,6-tetrahydro-2(l//)-py-rimidinone in tetrahydrofuran converted cyclopropyl ketones 13 to ring-cleaved ketones 16 via cyclopropylmethyl-type radicals. 

---