Methoxycarbonylation group

Barrelene was obtained via a double Diels-Alder reaction from a-pyrone with methyl acrylate (H.E. Zimmerman, I969A). The primarily forming bicyclic lactone decarboxylates in the heat, and the resulting cyclohexadiene rapidly undergoes another Diels-Alder cyclization. Standard reactions have then been used to eliminate the methoxycarbonyl groups and to introduce C—C double bonds. Irradiation of barrelene produces semibullvalene and cyclooctatetraene (H.E. Zimmerman. 1969B). 

In the pyrrole series, ester groups a to nitrogen are more readily hydrolyzed by alkali, but those in a /3 position more readily by acid. A methoxycarbonyl group in the 2-positlon is meta directing thus bromination yields mainly 4-bromo-2-methoxycarbonylpyrrole. Free radical chlorination with f-butylhypochlorite gives the 5-chloro derivative. 

BRP2307177). The bromine atom of 203 was also replaced by a methoxy and a cyano groups with NaOMe in the presence of Cu(I)I and with Cu(I)CN to give compounds 205 and 206, respectively. The nitrile group of 206 was converted into a methoxycarbonyl group to give compound 207. 

In some cases, no cycloalky ladon is observed by the reacdon of uittomethane v/ith electron-deficient olefins v/ilh cyano and methoxycarbonyl groups The reacdon affords new, highly fiincdonalLzed cyclohexenes in the presence of catidydc amount of piperidine under solvent- free conchdons v/ith focused microwave irradiadon fEq 7 41 ... 

Although intermediate 2 is terminated at both ends by electrophilic carbonyl groups, the aldehydic function at C-7 is inherently more reactive, and thus more susceptible to a nucleophilic attack, than the methoxycarbonyl group at C-l. As a result, it should be possible to selectively engage the aldehyde carbonyl of intermedi-... 

Vinyl radicals can also participate in 6-exo cyclizations. In pioneering work, Stork and his group at Columbia University showed that stereoisomeric vinyl bromides 20 and 21 (see Scheme 3) can be converted to cyclohexene 22.7 The significance of this finding is twofold first, the stereochemistry of the vinyl bromide is inconsequential since both stereoisomers converge upon the same product and second, the radical cyclization process tolerates electrophilic methoxycarbonyl groups. The observation that the stereochemistry of the vinyl bromide is inconsequential is not surprising because the barrier for inversion of most vinyl radicals is very low.8 This important feature of vinyl radical cyclization chemistry is also exemplified in the conversion of vinyl bromide 23 to tricycle 24, the key step in Stork s synthesis of norseychellanone (25) (see Scheme 4).9 As in... 

An acetyl group in the 2-position favors the monocyclic structure presumably because of the resonance stabilization.12 The same observation was made with oxepin-2,7-dicarbaldehyde, oxepin-2,7-dicarboxylic acid, and oxepin-2,7-dicarbonitrile.23 Substituents in the 4- and 5-positions of the oxepin such as methyl or methoxycarbonyl groups shift the equilibrium towards the epoxide.12 24 Low temperature 1H NMR studies on 7-ethyloxepin-2-carbonitrile and ethyl 7-ethyloxepin-2-carboxylate established a nonplanar boat geometry with a ring-inversion harrier of 6.5 kcal mol-1.25... 

With an octamcthylcne chain it is possible to bridge the two carbon atoms adjacent to the oxygen. On heating, the expected oxepin 10 with methoxycarbonyl groups in the 4- and 5-position is formed in 95% yield.132... 

Dichloro- and l,2-dibromo-l,2-dihydro-3-benzoxepins are dehalogenated with zinc in methanol to give 3-benzoxepin (6a) in excellent yield.93 A methoxycarbonyl group in the 2-position, however, diminishes the yield of 6b considerably.91... 

Bulky substituents make it possible to prepare a stable 8n-electron thiepin. For that purpose, the methoxycarbonyl groups of furanothiepin 6 (R = C02Me) are converted with methylmagne-sium bromide to the corresponding diol (R = CMe2OH) which reacts spontaneously with N-phenylmaleimide to give the thermally stable endo-thiepin 8.67 Quantitative desulfurization is achieved in the presence of triphenylphosphane. 

Vinyl sulfones such as 262 are smoothly converted to a,) -unsaturated nitriles such as 263 on treatment with KCN in the presence of dicyclohexyl-18-crown-6 in refluxing t-butyl alcohol (equation 155)148. The reaction conditions are compatible with base-labile functionalities such as a methoxycarbonyl group (equation 156)148. This method can be used in the preparation of the sesquiterpene aldehyde nuciferal from allyl phenyl sulfones. 

Bicychc pyrazinones foimd in several natural products were synthesized via Michael addition of heterocyclic amines to nitro olefin followed by reduction/cyclization of the nitro group of the adduct [20] (Scheme 5). Further elaboration of the C-6 methoxycarbonyl group in pyrazinone to the n-propyl guanidine group could result in the synthesis of indoloperamine. 

Jones and Vogel investigated the snbstitnent effect of a 5,6-bis(methoxycarbonyl) group in bicyclo[2.2.2]octene (48i) [117]. The substituent effect of a single 5-exo substituent on the facial selectivities of bicyclo[2.2.2]octenes 48b-48h was also characterized by our group [118]. Epoxidation and dihydroxylation of the olefin moiety of 5-exo-substituted... 

Unsubstituted benzobicyclo[2.2.2]octatriene 76a bearing two methoxycarbonyl groups at the and C3 positions exhibited strong anti preference (with respect to the benzene moiety) with two oxidative electrophilic reagents, m-chloroperbenzoic acid (mCPBA) and osmium tetroxide. 

Entry 4 shows the reaction of 9-(E-2-butenyl)-9BBN with methyl pyruvate. This reaction is not very stereoselective, which is presumably due to a modest preference for the orientation of the methyl and methoxycarbonyl groups in the TS. Only use of an extremely sterically demanding pyruvic ester achieved high diastereoselectivity. 

Recently, Reinhoudt and Kouwenhoven 53) have reported, in connection with their successful synthesis of monocyclic thiepin 87, that the relatively high stability of 87 is attributed to the presence of the two methoxycarbonyl groups which cause a decrease in the electron density of the 8n-electron system. As a result, the formal anti-aromatic character is reduced. Traynelis and his coworkers 6) have also reported a slight increase in the thermal stability of benzo[6]thiepin when electron-withdrawing groups are present. These conclusions have subsequently been supported by resonance energy calculations on various thiepin derivatives59). Thus, the re-... 

In some cases, no cycloalkylation is observed by the reaction of nitromethane with electron-deficient olefins with cyano and methoxycarbonyl groups. The reaction affords new, highly functionalized cyclohexenes in the presence of catalytic amount of piperidine under solvent-free conditions with focused microwave irradiation (Eq. 7.41).42... 

Reaction of ester 521 with PTAD gives a single adduct 522, formed by the addition of the dienophile syn to the methoxycarbonyl group. In contrast, the free diol 518 provides a mixture of adducts 519 and 520 in a 1 6 ratio. This result can be rationalized by a hydrogen bonding of the hydroxy groups with the dienophile (Scheme 88) <1995J(P1)2647>. 

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