2,6-Cycloheptadienone

The photolysis of protonated 2,6-cycloheptadienone (73) and its 5-methyl derivative (74) at — 78° in FHSOs yields as a single product in each case the corresponding protonated vinylcyclopentadienones 75 and 76, wliich subsequently isomerize thermally to the more stable cations 77 and 78 (Noyori et al., 1972). 

Bottini and Gal (81) added 2,6-cycloheptadienone (148), prepared from cycloheptanone in four steps (82), to a solution of methanolic methylamine and obtained tropinone (124) in 64% yield (Scheme 6). This reaction was suggested long ago by Robinson (66). 

Macdonald and Dolan have reported a new route to the tropinone system (88). 2-Cyclohexenone (160) is transformed to 2-[(trimethylsilyl)oxyl]-l,3-cyclohexadiene (161), and then by dichlorocyclopropanation to 162 and by acid-catalyzed hydrolysis to 2-chloro-2,6-cycloheptadienone (163). Addition... 

Stoichiometrically protonated cycloheptadienones appear to undergo electrocyclic ring-opening/ring-closure processes R. Noyori, Y. Ohnishi and M. Kato, J. Am, Chem. Soc., 94, 5105 (1972). 

In a noteworthy series of studies, Herndon has shown that cyclopropylcarbenes can be used as four-carbon components in molybdenum- and tungsten-mediated [4 + 2 + l]-reactions with alkynes and carbon monoxide (CO). These reactions give cycloheptadienones in moderate yields and with moderate selectivity (Equations (26)—(28)). The mechanism of this reaction is proposed to proceed through a series of steps involving metathesis, GO insertion, ketene formation, cyclopropane cleavage, and finally reductive elimination (Scheme 43).133... 

The first metal-catalyzed [4 +2]-reaction of tethered dienes with 7r-systems was reported by Wender and Jenkins using alkynes initially as the two-carbon component.21 This study was based on the earlier observation by Wender and Ihle that in the [4 + 4]-cycloaddition of bis-dienes a competing side-reaction is the [4 + 2]-cycloaddition of the diene with a mono-ene portion of a second diene. The extension of this reaction to the synthesis of seven-membered rings by trapping the metallacycloheptadiene with CO, a formal [4 + 2 + l]-cycloaddition, has been shown in preliminary studies to be feasible. For example, tethered diene-yne 160 can be converted to cycloheptadienone 163 in an Rh(l)-catalyzed [4 + 2 + l]-reaction with CO, albeit the [4 + 2]- and [2 + 2 + l]-reaction products dominate (Equation (29)). The mechanistic scheme (Scheme 44) illustrates the possible metallacyclic intermediates leading to the observed products and provided the conceptual basis for the realization of three novel reaction types ([4 + 2], [2 + 2 + 1], and [4 + 2 + 1 ]).1... 

An alternative approach to [3 + 2 + 2]-cycloadditions has been reported by Saito and co-workers and involves cleavage of a methylenecyclopropane to produce, after capture with two alkynes, the cycloheptadiene products shown in Scheme 54.144 In a mechanistically distinct [3 + 2 + 2]-reaction, Murakami and Miura report a route to a cycloheptadienone involving the capture of two alkynes initiated by a Suzuki coupling to 2-cyanophenylboronic acid (Equation (32)).145... 

This reaction can be used to effect a [3 + 2] or a [3 + 2 + 2] annelation to a cyclopentenone ketal or a cycloheptadienone ketal, respectively. Thus the adduct of a vinylcuprate with 1 rearranges thermally (240-290°) to 3-cyclopentenone ketals (3) in 50-80% yield (equation I). [3 + 2 + 2]Annelation involves preparation of... 

Fig. 2.32. Possible mechanism of the formation of cyclopentenones and cycloheptadienones from alkoxy(cyclopropyl)carbene complexes [373],...

The formation of cycloheptadienones from alkoxy(cyclopropyl)carbene complexes and alkynes (Entry 5, Table 2.24) [388,389] proceeds essentially by the same mechanism as the Dotz benzannulation reaction (see Figure 2.32). The cyclopropyl group participates in the electrocyclic rearrangement as the equivalent of a vinyl group. 

It has recently been reported (8) that irradiation of dilute solutions of 3,5-cycloheptadienone (XXXVII) and its 2-methyl derivative gives rise... 

Irradiation of 5-methoxy-2,4-cycloheptadienone (Formula 140) gives the bicyclic ketone (Formula 141) (59). Eucarvone (Formula 142) gives a... 

Irradiation of 3,5-cycloheptadienones (Formula 156) (R = H or Me) in ether solution gives carbon monoxide and a 1,3,5-triene (Formula 157)... 

Formula 375 (165). Substituents seem to exert relatively little effect on the photoisomerization of 1,3-cycloheptadiene. Thus irradiation of 1,4-diphenyl-l,3-cycloheptadiene (166), 5-methoxy-2.4-cycloheptadienol (161,162), 2,4-cycloheptadienol (161,162), 5-methoxy-2,4-cyclohepta-dienone (161,162), and eucarvone (60) gives in each case the bicyclic photoisomer. Eucarvone gives other products as well (see Sec. II,C). The only exceptions to the generality of the photoisomerization of 1,3-cycloheptadienes encountered so far is the irradiation of 3,5-cyclohepta-dienone (Formula 376) (R = H) and 2-methyl-3,5-cycloheptadienone (Formula 376) (R = Me) which give 1,3,5-hexatriene (Formula 377)... 

The formation of polysubstituted cycloheptadienones depicted in Eq. (5.334) constitutes the first example of an acid-induced ketene-diene cycloaddition.908... 

The 1,3-cyclohexadiene complex 66 was expanded to cycloheptadienone (80) by an interesting reaction of CO mediated by AICI3 via 79. The bicyclo[3.2.1]octenedione 81 was prepared by the twofold carbonylation of 66 under high pressure of CO via the intermediate 79 [22,23], This interesting transformation has been applied to the stereoselective construction of the dicyclopenta[a, JJcyclooctene core 83 of ceroplastin terpene from 82 under 5 atm of CO [24],... 

Stereospedfic photodecarbonylation of ris- and trans-2,7-dimethyl-3,5 -cycloheptadienone observation of an apparent symmetry-forbidden concerted cheletropic fragmentation. Journal of the American Chemical Society, 105, 2900-2901. 

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