Cyclobutanol 2-methyl

This mechanism also has the advantage that the same intermediate can be postulated for the production of 1-methyl cyclobutanol.6... 

P additive, cm. C2H4 Acetone 1-Methyl-cyclobutanol 1-M ethyl-cyclobutanol/ acetone... 

The formation of 1-methyl cyclobutanol was observed in the photolysis of 2-pentanone at 3130 A, and later in the wavelength region 2300-3200 A, also. ... 

The failure to identify 1-methyl cyclobutanol in previous investigations can be traced to analytical difficulties. 

Yang and Yang reported the formation of 12 % 1-methyl cyclobutanol in cyclohexane at room temperature. The identification was made by the gas chromatographic retention time and the infrared spectrum. 

A similar example is the ring expansion of cyclobutanone via l-tris(methylsulfanyl)methyl-cyclobutanol (6) to 2,2-bis(methylsulfanyl)cyclopentanone (7).43 The use of Af,A-diisopropyl-ethylamine is unneccessary in this reaction as the hydroxy group has already been deprotonated with butyllithium. Further examples of this type of reaction can be found in refs 43 and 44. 

A consequence of the orientation of the 11-carbonyl function towards the C-19 methyl group which is retained in the excited state is the exclusive functionalization at C-19. Ring cleavage products of the Norrish II type are not observed but the reaction is rather sensitive to conformational changes in the substrate. In a series of experiments conducted under comparable conditions (24 hr irradiation) the yield of cyclobutanols drops... 

In some cases, the Grignard reaction can be performed intramolecularly. For example, treatment of 5-bromo-2-pentanone with magnesium and a small amount of mercuric chloride in THE produced 1-methyl-1-cyclobutanol in 60% yield. Other four- and five-membered ring compounds were also prepared by this procedure. Similar closing of five- and six-membered rings was achieved by treatment of a 6- or s-halocarbonyl compound, not with a metal, but with a dianion derived from nickel... 

A lower molecular weight methyl ketone and an olefin are isolated as products of this reaction. That the enol is formed as a primary product which rearranges to the ketone follows from its detection in the IR spectrum of gaseous 2-pentanone upon photolysis. 3 In addition to the ketone and olefinic products, one usually obtains varying amounts of cyclobutanols. 

That the situation is different for photochemical reactions is indicated by a particularly interesting recent study of some dialkylketones (239). In solution, 5-nonanone, 152, reacts photochemically to yield the cyclobutanol 153 and its isomer 154 in comparable amounts. Within the urea clathrate, however, 153 is the dominant product, with only traces of 154 being formed. The cyclobutanols analogous to 153, that is, having methyl and hydroxyl cis, also predominate in the urea-clathrate-mediated photocyclization of 2-hexanone and 2-undecanone. It might be expected that the bulky cyclobutane derivatives, which almost certainly cannot be crystallized in a urea clathrate, would also not be formed in such a clathrate. There are decomposition pathways (cleavage reaction 0 of the diradical intermediate that occur both in the clathrate and in solution. Nevertheless, the ring closure is a major pathway of reaction even in the clathrate. 

Once again additional methyl groups alter the reaction path. iro/o-2-Acetyl-3,3-dimethylnor-bornane (4) affords 6,8,8-trimethylspiro[4.3]oct-2-en-6-ol (5) via two consecutive intramolecular H-abstraction sequences, while the corresponding two-isomer 6 affords the expected cyclobutanol 7 directly.6... 

Byproducts of this rearrangement are cyclobutenes, cyclopropane derivatives and allenic alcohols. The ratio of these products depends on the substitution of the substrate and on the reaction conditions. For example, 3-methyl-5-tosyloxypenta-l,2-diene (3) gives 75% of 1-methyl-2-methylenecyclobutanol (4) upon hydrolysis with water and calcium carbonate at 100 °C, while acetolysis with acetic acid/sodium acetate at 80 °C, and subsequent treatment with lithium aluminum hydride, provides only 37% of the cyclobutanol.12... 

Norrish discovered the cleavage reactions (E of Eq. 4) of excited state ketones to methyl ketones and olefins [257]. It was later recognized by Yang and Yang [258] that the biradical intermediates (BR) can also cyclize (C) to yield cyclobutanols. 

The substitution of a methyl group at carbon 3 of the adamantyl group of 86b (designated 89) lowers the molecular symmetry and makes conceivable the formation of three cis and three trans cyclobutanol photoproducts. Of these, only two cis (90 and 91) and two trans (92 and 93) isomers could be... 

Since the volume of a methyl group is slightly larger than that of a hydroxyl, the lack of the cis cyclobutanol may result from an inability of its precursor... 

The data in Table 15 reveal that the values of E/C ratios from the solid p-CD complexes are always lower than from benzene solutions. The degree to which the cis cyclization products are favored over the trans increases from 103a to 103e as expected from the model in Scheme 46. Also, the longer homologue of each ortho-, meta-, and para-methylated 103 yields the greater amount of cyclobutanols when irradiated in solid P-CD complexes. Thus, Scheme 46 explains qualitatively the photoproduct ratios from solid p-CD. 

In contrast, the chirally modified zeolite approach led to poor results. For instance, irradiation of the methyl ester of 2-benzoyladamantane-2-carboxylic acid 44, included in the NaY zeolite, which had been preloaded with optically pure ephedrine as a chiral inductor, gave the cyclobutanols 45 and 46 in 35 and 5% ee, respectively (Scheme 11) [65]. Similarly, the methyl ester of benzoylcyclohexane carboxylic acid 47 afforded the cyclobutenol 48 in 30% ee [63]. 

Cyclobutanol IV/4, 110 Cyclopropan 1 -Hydroxy-1 -methyl-XIIl/2a, 460, 462 E17a, 301 (R - COOR + TiX4/R - MgX) Ether Ethenyl-ethyl- Vl/ld, 147ff. Furan Tetrahydro- Vl/lb, 611 f. (Jeger-Reakt.) VI/3, 529/536 (Cyclokond.)... 

Three successive [2+4] cycloadditions were used in the synthesis of the pentacyclic methyl ether of G-2N by Kraus and Zhao [92] and later, by a slightly modified procedure, also of the natural product G-2N (118) [93] (Scheme 31). Thermal reaction of the cyclobutanol 112 with acrylic ester gave the dihydronaphthalene 113 which was demethylated by treatment with boron tribromide and converted into the exocyclic ketene acetal 114. This unstable diene was reacted in a second cycloaddition with 2,6-dichlorobenzoquinone (115) to afford the tetracyclic chloroquinone 116. In a last Diels-Alder reaction, ring E was anella-ted by treatment of 116 with l-methoxy-l,3-bis[(trimethylsilyl)oxy]-l,3-buta-diene (117) to yield the pentacyclic natural product G-2N (118) [93]. 

---