Abstract:BS8 ITSThe reactions of cyclopentadiene with cyclohexa-2.4-dienones of general structure (VII) have been shown to proceed by initial diene addition of the hydrocarbon to the 4,5-double bond of the cyclohexadienone. The resulting adducts, which are derivatives of tricyclo[6,2,1 ,O 2, ' 1 undeca-5,9-dien-4-one (111), rearrange even at room temperature to give products having the tricyclo[5,2,2,02~6]undeca-4,1 O-dien-8-one skeleton (I), but their intermediacy has been demonstrated by trapping experiments with phe… Show more
“…Though the above cycloaddition gave a single product apparently arising from π 4s (cyclohexadienone) + π 2s (cyclopentadiene) mode of addition, the cyclohexa-2,4-dienone 9 could react with cyclopentadiene to give many other adducts such as I and II (Figure ). It may also be mentioned that there exists a mechanistic dichotomy regarding the mode of addition and the mechanism of formation of the adducts during the cycloaddition of cyclohexa-2,4-dienones with dienes . The adduct of type 7 may also arise via 3,3-shift in the compounds of type I which may be formed during initial stages of cycloaddition. 14a-c However, we could not isolate the adducts of type I or II in this case.…”
Section: Resultsmentioning
confidence: 76%
“…It may also be mentioned that there exists a mechanistic dichotomy regarding the mode of addition and the mechanism of formation of the adducts during the cycloaddition of cyclohexa-2,4-dienones with dienes . The adduct of type 7 may also arise via 3,3-shift in the compounds of type I which may be formed during initial stages of cycloaddition. 14a-c However, we could not isolate the adducts of type I or II in this case. 2 3 …”
A novel, efficient and stereospecific synthesis of the marine
natural product capnellene from p-cresol
is described. Generation of
4-methyl-6,6-spiroepoxycyclohexa-2,4-dienone (9) from
5-methylsalicyl
alcohol (8), its in situ cycloaddition with cyclopentadiene
(in situ), and the photochemical oxa-di-π-methane reaction of an endo
tricyclo[5.2.2.02,6]undecenone are the key
features of our strategy.
An efficient synthetic route to appropriately designed endo
tricyclo[5.2.2.02,6]undecenones
(compounds 6, 11−13) endowed with most of the
structural and stereochemical features of capnellene,
from the keto epoxide 7, are described. The
photochemical reaction of 6, and 11b,d upon
sensitized
irradiation readily gave the oxa-di-π-methane products 5,
14, and 15 respectively. The
tetracyclic
compound 5 was elaborated to capnellene after cleavage of
the peripheral cyclopropane bond,
Barton's deoxygenation, deprotection of the carbonyl group, and Wittig
reaction.
“…Though the above cycloaddition gave a single product apparently arising from π 4s (cyclohexadienone) + π 2s (cyclopentadiene) mode of addition, the cyclohexa-2,4-dienone 9 could react with cyclopentadiene to give many other adducts such as I and II (Figure ). It may also be mentioned that there exists a mechanistic dichotomy regarding the mode of addition and the mechanism of formation of the adducts during the cycloaddition of cyclohexa-2,4-dienones with dienes . The adduct of type 7 may also arise via 3,3-shift in the compounds of type I which may be formed during initial stages of cycloaddition. 14a-c However, we could not isolate the adducts of type I or II in this case.…”
Section: Resultsmentioning
confidence: 76%
“…It may also be mentioned that there exists a mechanistic dichotomy regarding the mode of addition and the mechanism of formation of the adducts during the cycloaddition of cyclohexa-2,4-dienones with dienes . The adduct of type 7 may also arise via 3,3-shift in the compounds of type I which may be formed during initial stages of cycloaddition. 14a-c However, we could not isolate the adducts of type I or II in this case. 2 3 …”
A novel, efficient and stereospecific synthesis of the marine
natural product capnellene from p-cresol
is described. Generation of
4-methyl-6,6-spiroepoxycyclohexa-2,4-dienone (9) from
5-methylsalicyl
alcohol (8), its in situ cycloaddition with cyclopentadiene
(in situ), and the photochemical oxa-di-π-methane reaction of an endo
tricyclo[5.2.2.02,6]undecenone are the key
features of our strategy.
An efficient synthetic route to appropriately designed endo
tricyclo[5.2.2.02,6]undecenones
(compounds 6, 11−13) endowed with most of the
structural and stereochemical features of capnellene,
from the keto epoxide 7, are described. The
photochemical reaction of 6, and 11b,d upon
sensitized
irradiation readily gave the oxa-di-π-methane products 5,
14, and 15 respectively. The
tetracyclic
compound 5 was elaborated to capnellene after cleavage of
the peripheral cyclopropane bond,
Barton's deoxygenation, deprotection of the carbonyl group, and Wittig
reaction.
“…Reacting 2,4-cyclohexadienones 237 with cyclopentadiene as reaction partner only the adducts of the type 239 were isolated (Scheme 76). 116 The supposed primary cycloadduct 238 was not observed but could be intercepted if the cylcoaddition was done in the presence of one equivalent of phenylazide. Phenylazide is known to undergo [3 + 2] cycloaddition with slightly activated double bonds like the double bond in norbornene.…”
Section: Tandem Processes With the Sequence: Diels-alder Reaction Firmentioning
Diels-Alder reactions and sigmatropic rearrangements are of paramount importance in synthesis. The tandem Diels-Alder/ sigmatropic rearrangement processes combining these two powerful methods is presented in this review. Both possible sequences of this tandem process are discussed and several successful examples of the synthesis of natural products using the combination of these two reactions as key step demonstrate the utility of these processes.
“…There exists a mechanistic dichotomy 17,18 regarding the formation of the adducts and pericyclic modes during cycloaddition of cyclohexa-2,4-dienones with dienes. For instance, the adducts 18 − 20 could be obtained either via a direct primary mode of addition wherein the cyclohexa-2,4-dienones behave as a 4π partner and the diene as a 2π partner or via a 3,3-shift in the adducts of type I which may initially form during the cycloaddition as a result of π 4s (diene) + π 2s (dienone) addition. , However, the adducts of type I were not obtained in the above experimental conditions. 3 A list of the tricyclic adducts prepared by cycloaddition of various spiroepoxycyclohexa-2,4-dienones with dienes. 2 3 4 Some other possibile adducts during cycloaddition of spiroepoxycyclohexa-2,4-dienones.…”
Cyclohexa-2,4-dienones have been known for many years. 1 However, their chemistry has been limited to dimerization and rearrangement 1 until recently. [2][3][4][5] This is presumably because of their instability and high reactivity toward themselves and their propensity to aromatization and rearrangement. 1 In context with a research program to develop a unified strategy for the synthesis of polyquinanes and protoilludanes which has generated considerable interest, 6,7 cycloaddition of in situ generated spiroepoxycyclohexa-2,4-dienones of type 1 was explored 4,5 and a route to a variety of annulated bicyclo[2.2.2]octenones of type 2 and 3 was developed. Chemical and photochemical reactions of the annulated bicyclo[2.2.2]octenones thus obtained were also investigated. This led to the development of routes to various carbocyclic structures of contemporary interest 6,7 such as linearly fused cis-anti-cis triquinanes 4, cis-syn-cis triquinanes 5, tetraquinanes 6 and 7, protoilludanes 8, and the oxa-sterpurane framework 9 (Figure 1). In this Account, we summarize developments in this area wherein the spiroepoxycyclohexa-2,4-dienones have played a very important and crucial role, in conjunction with the chemical and photochemical reactions of the resulting tricyclic frameworks.Generation of Spiroepoxycyclohexa-2,4-dienones In Situ and Intermolecular π 4s + π 2s Cycloaddition with Cyclic Dienes. (a) Synthesis of endo Tricyclo[5.2.2.0 2,6 ]-undecanes. Conceptually, the tricyclo[5.2.2.0 2,6 ]undecanes of type 2 should be directly accessible in a single step via cycloaddition of cyclohexa-2,4-dienones such as 10 or 11 (Scheme 1) with appropriate olefins. Although the parent cyclohexa-2,4-dienone 10 (the keto tautomer of phenol) is unknown, only a few methods are known 8-10 for the preparation of 6,6-dialkyl derivatives 11 such as alkylation of substituted phenols 8 and rearrangement 9 of the exocyclic epoxide derived from dimethylfulvene. However, these methods appeared to be unsuitable for the above purpose. Therefore, a new indirect sequence for the synthesis of tricyclo[5.2.2.0 2,6 ]undecanes of type 2 employing epoxycyclohexa-2,4-dienones of type 1 was developed. It was envisaged that cycloaddition of 1 with cyclopentadiene would furnish adducts of type 14 ( Figure 2) whose epoxyketone moiety and olefinic bond present in the five-membered ring would be readily manipulated to give a variety of tricyclo[5.2.2.0 2,6 ]undecanes of type 2. However, spiroepoxycyclohexadienones of type 1 have only a fleeting existence during the oxidation of ohydroxymethyl phenols and instantaneously dimerize. 11 Therefore, it was thought to generate the spiroepoxycyclohexa-2,4-dienones via a retro Diels-Alder reaction of the readily obtainable 11 epoxydimers 13, and intercept them with a suitable diene/olefin.Unfortunately, pyrolysis of dimers of type 13 in the presence of dienes/olefins failed to yield adducts of type 14 and gave the corresponding aldehyde instead (Scheme 2). This is apparently due to the thermal rearrangement of the oxira...
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