1 - methyl-1 -cyclobuten

Bei der Bestrahlung von 1-Methyl-cyclobuten (25) in Aceton mit Licht der Wellenlange A = 254 m[ji werden nur Carbonyl-Verbindungen isoliert, unter denen das 6-Methyl-5-hepten-2-on (26) das Hauptprodukt darstellt. 

Examples of this are the photocycloaddition reactions of 3-methylcyclohex-2-enone with ethene96 and isophoronc with l-propen-2-yl acetate.97 The cycloaddition of isophorone to methyl cyclobutene-1-carboxylate98 or of ( —)-piperitone (28) to 1,2-bis(trimethylsiloxy)cyclo-butene (29)99 affords tricyelo[4.4.0.02 5]deean-7-ones, used as starting compounds in fragmentation reactions. 

CYCLOADDITION Alumina chloride. l,2-Bis(trimethylsilyloxy)cyclo-butene. 2,2-Dimcthyl-3(2//)-furanone. Lthylaluminum dichloridc. Kctcnc diethyl acetal.. Methyl cyclobutene-carboxylate. Trimethyl-1,3-dioxolen-one. Zinc chloride. 

Our enthalpy of formation archive lacks data for the corresponding cyclobutene/cyclo-butane derivatives. Nonetheless, the enthalpy of hydrogenation22 of both 1-methyl-cyclobutene and methylenecyclobutane in the same solvent (AcOH) has been reported. Because the same product, methylcyclobutane, is formed, it is not unreasonable to assume that the difference of the enthalpies of hydrogenation of the two olefins roughly equals the difference of the enthalpies of formation of the olefins66. It is thus found that the... 

Cyclopenten 2-Hydroxy-l-phenyl-3,4,5-trioxo- E15/2, 1453 f. (Dioxo-methyl-cyclobuten/Oxid.)... 

Example 6.2. The thennal ring opening of cis-3-chloro-4-methyl-cyclobutene, a conrotatory process. 

Pentacarbonyl-(trifluor-chlor-athyl)- 1428 Pentacarbonyl-[5-triphenylstannyl-tetrakis-[trifulor-methyl]-cyclobuten-(2)-yl - 1429... 

Studies of the asymmetric photocycloadditions of the 1,3-dioxacyclohexenones (-)-20 or (-)-23, respectively with methyl cyclobutene opened a new route for the syntheses of enantiomerically pure (—)- and (-i-)-grandisol (19)81,82. This approach adopts the use of stereofacial differentiation by a rigid spirocyclic arrangement of the auxiliary and the enone. Since the alkene adds preferentially to face a of both enones, (— )-20 and (—)-23, Complementary enantiomeric product channels are available operating from a single enantiomer of the auxiliary in each case. The photocycloaddition reactions proceeded in a head-to-head fashion (HH/HT 7 1 at — 78 °C) to give tricyclic products with cis-anti-cts stereochemistry ( + )-21 and (+)-24, respectively. The auxiliary, ( —)-menthone, was smoothly removed by formic acid treatment of the cycloadduct (+)-21, no epimerization of the acetyl group in (— )-22 was observed under these mild conditions. 

Other monocyclic monomers will imdergo ring-opening reactions cyclobutene and 1-methyl cyclobutene produce polybutadiene and cis-polyisoprene, respectively but this synthetic route cannot compete with estabhshed methods for preparing synthetic elastomers. Reactions are slower with the larger rings, as the strain decreases, but a useful elastomer with a high trans content and well-developed crystallinity (such as the product sold under the trade name Vestenamer) can be prepared from cis-cyclooctene (the trans compound is umeactive). 

Figure 6. Degree of polymerization ( ) and polydispersity (O) resulting from ring-opening metathesis polymerizations of (a) 5- [8 -[4"-(4" -nitrostilbeneoxy)octyl]carbonyllbicyclo[2.2.1]hept-2-ene and (b) poly[3-((8 -(4"-(4" -nitrostilbeneoxy)octyl)carbonyl)methyleneoxy)methyl]cyclobutene) initiated by RuCl2(CHPh)(PPh3)2 in CH2CI2 at 25 and 45 °C, respectively [187].

Figure 18. Transition temperatures from the glass ( ), crystalline (o), nematic (A) and smectic ( ) phases of poly 5- [n-[4"-(4" -nitrostilbeneoxy)alkyl]carbonyl )bicyclo[2.2. l]hept-2-ene)s (DP =27-42, pdi= 1.08-1.11) [187], 4-n-alkoxy-4 -nitro(stilbene) [228] and poly[3-[(( -(4 -(4"-nitrostilbeneoxy)alkyl)carbonyl)methylene-oxy)methyl]cyclobutene s (DP =61 -72, pdi= 1.14-1.16) [187] as a function of the number of methylenic carbons in their n-alkyl spacers.

Describe metathesis polymerization of methyl cyclobutene, showing the mechanisms of initiation and propagation. 

It should be noted that there are two ways of incorporating bicyclo-2,2,l-octene units into polymers. It is necessary to consider the distributions of the asymmetric centers present in polymers derived from this monomer in addition to considering the cis and trans structures present, to completely interpret the spectra of polymers derived from bicyclo-2,2,1-octane. Polymers derived from unsymmetrical cyclic olefins, in general, should not be e3q>ected to be stereoregular. However, cmr and pmr studies of polymers derived from 1-methyl cyclobutene and 1-methyl-trans-cyclooctene have predominantly head-tail structures [93,94]. Since they contain both cis- and trans- inits, they can be considered to be stereoregular copolymers. 

The methyl cyclobutene on photo-oxygenation gives regioselective products. 

An olehn metathesis reaction has been effected by photochemical [2 + 2] cycloaddition followed by thermolysis of the cyclobutane (Scheme 17). Thus thermolysis of the tricyclic c ,a ft,c/5-adduct (57) gave the cyclodeca-1,5-diene skeleton (58) present in germacranolides (Scheme 17). A closely related process is the [4C + 2C] annelation which has been utilized in the synthesis of lO-epi-juneol (61) (Scheme 18). The photoadduct (59) from piperitone and methyl cyclobutene-1-carboxylate was converted in four steps into the tricyclic compound (60). The strained tr-bond in (60) was cleaved with lithium naphthalide to give 10-epi-juneoI (61). ... 

This method assumes that RRKM theory (or some other theory) correctly models the energy dependence of the unimolecular rate constants. In order to apply RRKM theory, the unimolecular reaction must be well defined and the threshold energy must be known. The experimental rate constants, — A m[M](D/5), are measured for a wide range of pressure. The collisional rate is /cm[ ]j D is the experimental yield for the decomposition product, and S is the yield of the collisionally stabilized product. A recent study for HCl from 1-, 2-, and 3-methylchlorocyclobutane will be given as an example. The rate constants for the isomerization of 3-methyl-cyclobutene formed via HCl elimination from 3-methylchlorocyclobutane are shown in Figure 2.2. The 3-chloromethylcyclobutane was activated by... 

A more conventional cycloaddition occurs with activated acetylenes, however, the intermediate cyclobutene adducts undergo rearrangement to give insertion of two carbon atoms into the enamine chain (55). Thus the enamine (16) reacted with methyl propiolate to give the dienamino ester (73), presumably via the cycloaddition product (65a). 

The synthesis of 2-chloro-2,3,3-trifluorocyclobutyl acetate illustrates a general method of preparing cyclobutanes by heating chlorotrifluoroethylene, tetrafluoroethylene, and other highly fluorinated ethylenes with alkenes. The reaction has recently been reviewed.11 Chlorotrifluoroethylene has been shown to form cyclobutanes in this way with acrylonitrile,6 vinylidene chloride,3 phenylacetylene,7 and methyl propiolate.3 A far greater number of cyclobutanes have been prepared from tetrafluoroethylene and alkenes 4,11 when tetrafluoroethylene is used, care must be exercised because of the danger of explosion. The fluorinated cyclobutanes can be converted to a variety of cyclobutanes, cyclobutenes, and butadienes. 

Since 3-methylenecyclobutane-l,2-dicarboxylic anhydride is easily converted to 3-methyl-2-cydobutene-l,2-dicarboxylic acid, it is an intermediate to a variety of cyclobutenes. The dimethyl ester of 3-methylenecyclobutane-l,2-dicarboxylic acid is also a versatile compound on pyrolysis it gives the substituted allene, methyl butadienoate, and on treatment with amines it gives a cyclobutene, dimethyl 3-methyl-2-cyclobutene-l,2-di-carboxylate. ... 

Scheme 10.2 gives some examples of ene and carbonyl-ene reactions. Entries 1 and 2 are thermal ene reactions. Entries 3 to 7 are intermolecular ene and carbonyl-ene reactions involving Lewis acid catalysts. Entry 3 is interesting in that it exhibits a significant preference for the terminal double bond. Entry 4 demonstrates the reactivity of methyl propynoate as an enophile. Nonterminal alkenes tend to give cyclobutenes with this reagent combination. The reaction in Entry 5 uses an acetal as the reactant, with an oxonium ion being the electrophilic intermediate. 

Reinhoudt et al.53) have reported the first synthesis of a monocyclic thiepin stabilized by electronic effects of the substituents. This synthesis utilizes the idea described in Section 2.3.3. 3-Methyl-4-pyrrolidinothiophene (85a) was treated in deuteriochloroform at —30 °C with dimethyl acetylenedicarboxylate. H-NMR monitoring of the reaction indicated that a [2 + 2]cycloaddition proceeded slowly at this temperature giving the 2-thiabicyclo[3.2.0]heptadiene (86a) which rearranged via ring opening of the cyclobutene moiety to the 4-pyrrolydinylthiepin (87a). At the... 

Tributylstannyl)-3-cyclobutene-1,2-diones and 4-methyl-3-(tributylstan-nyl)-3-cyclobutene-l,2-dione 2-ethylene acetals undergo the palladium/copper-catalyzed cross coupling with acyl halides, and palladium-catalyzed carbon-ylative cross coupling with aryl/heteroaryl iodides [45]. The coupling reaction of alkenyl (phenyl )iodonium triflates is also performed by a palladium/copper catalyst [46],... 

The sesquiterpenes (+)-10-epijuneol466, (4.54) and ( )-calameon467) (4.55) have been obtained via addition of 6-isopropyl-3-methyl-2-cyclo-hexenone to cyclobutene derivatives. A similar sequence has been applied for the synthesis of an eudesmane precursor (4.56)468). 

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