Photochemical reactions methoxycarbonylation

In contrast to the metal-catalyzed reactions, photochemically generated methoxycarbonyl-trimethylsilylcarbene cyclopropanates styrene and 1-hexene with a slight Z-selectivity. While the preference for the sterically more congested cyclopropane is somewhat surprising, the rather... 

Oxidation of 4-methoxycarbonyl-2-methoxyphenol (421) with PhI(OAc)2 in MeOH was carried out in the presence of cyclopentadiene (CPD) to afford in 87% yield a Diels-Alder adduct 434, which was subjected to photochemical reaction followed by Ac20-BF3-Et20 treatment to give a linear triquinane 435 (47.6% in 2 steps). ... 

The protoberberine alkaloid, xylopinine, has been synthesized in an optically active form by Kametani et al.22 ). A key reaction in this synthesis was the photochemical cyclization of the optically active amino acid derivative 1,2,3,4-tetrahydro-6,7-dimethoxy-3-methoxycarbonyl-1 -methylene-2-veratroylisoquinoline with 1,3... 

Oxa-l -silabicyclo[ . 1,0 alkanes (n = 3 111 n = 4 113) were the only products isolated from the photochemical, thermal or transition-metal catalyzed decomposition of (alkenyloxysilyl)diazoacetates 110 and 112, respectively (equation 28)62. The results indicate that intramolecular cyclopropanation is possible via both a carbene and a carbenoid pathway. The efficiency of this transformation depends on the particular system and on the mode of decomposition, but the copper triflate catalyzed reaction is always more efficient than the photochemical route. For the thermally induced cyclopropanation 112 —> 113, a two-step noncarbene pathway at the high reaction temperature appears as an alternative, namely intramolecular cycloaddition of the diazo dipole to the olefinic bond followed by extrusion of N2 from the pyrazoline intermediate. A direct hint to this reaction mode is the formation of 3-methoxycarbonyl-4-methyl-l-oxa-2-sila-3-cyclopentenes instead of cyclopropanes 111 in the thermolysis of 110. 

Benzophenone (Amax = 340 nm, log e = 2.5, n-ir electronic transition) can be used as a photochemical reagent and eq. 4.25 shows a radical Michael-addition reaction with benzophenone. The formed benzophenone biradical (triplet state, Tx) abstracts an electron-rich a-hydrogen atom from methyl 3-hydroxypropanoate (62) to generate an electron-rich a-hydroxy carbon-centered radical [III], then its radical adds to the electron-deficient (3-carbon of a, (3-unsaturated cyclic ketone (63) through the radical Michael addition. The electrophilic oxygen-centered radical in the benzophenone biradical abstracts an electron-rich hydrogen atom from methyl 3-hydroxypropanoate (62) [70]. So, an a-hydroxy carbon-centered radical [III] is formed, and an electron-deficient a-methoxycarbonyl carbon-centered radical [III7] is not formed. 

Cyclobutane formation, occasionally in fairly low yield due to ring-opening reactions, also occurred by photochemical [2 - - 2] cycloaddition of vinylcyclopropane derivatives to an a, -unsaturated ketone moiety, " a cyclobuta-1,3-diene, a 1,4-benzoquinone, 2-acylthiophenes, and on irradiation of e t/o,enr/o-2,4-bis[( )-2-(methoxycarbonyl)vinyl]bi-cyclo[1.1.0]butane. A formal [2-1-2] cycloaddition also occurred on reaction of tricyclo[3.1.0.0 ]hex-3-ene with methyl 6-oxo-5-phenyl-l,3,4-oxadiazine-2-carboxylate to give methyl 9-oxo-10-phenyl-8-oxapentacyclo[4.4.0.0 ". 0 .0 °]decane-7-carboxylate, albeit in very low yield, after nitrogen extrusion. ... 

Finally, two syntheses of desethyl-ibophyllidine (674), by Bosch and collaborators, may be described. In the first of these (396,397), the tetracyclic tetrahydrocarbazole derivative 739 was constructed, as outlined in Scheme 112. The 6,7-bond was then formed by a tandem Pummerer re-arrangement-cyclization reaction, the phenylthio group was removed from the product 740 by hydrogenolysis, and the synthesis was completed by photochemical rearrangement of the methoxycarbonyl group. 

Heptakis 6-0-t-butyldimethylsilyl-P-cyclodextrin, on reaction with 4-chloro-methyl-A -methyl-2-nitroaniline, affords the mono-3-substituted benzyl ether. P-Cyclodextrin carrying a 2-(naphthylmethyl) group at 0-6 exists with the aromatic rings within the cavity to an extent which is very temperature dependent. Temperature can therefore be used to control the degree of complexing of the aromatic system with a fluorescent naphthalene compound. Heptakis-[2,3-di-0-acetyl-6-deoxy-6-iodo]-P-cyclodextrin treated with 6-methoxycarbonyl-2-naphthol allowed access to the compound having naphthoic acid substituents at all of the primary positions, and this forms a very stable 1 1 complex with a merocyanine laser dye which is a mimic of the antenna function in photosynthesis and shows promise as a photochemical microreactor. Mono-[6-0-(8-qui-nolyl)]-P-cyclodextrin has been reported, and the stabilities of inclusion complexes with amino acid guests have been described. ... 

A limiting stage of reaction (Equation 3.67) is NO diffusion into a polymeric matrix. The rate of reaction (Equation 3.68) should depend much more on the mobility of macromolecular reagents. Therefore, the distinction in the composition of radicals in PMMA photolysed at room temperature and 383 K is observed. At room temperature, acylalkylaminoxyl radicals are formed due to acceptance of low-molecular methoxycarbonyl radicals COOCHj by nitroso compounds. At 383 K, when molecular mobility essentially grows, dialkylaminoxyl radicals Rj-NO -R are formed because the meeting of two macromolecular particles occurs. The results obtained demonstrate an opportunity of using NO for elucidation of the polymer photolysis mechanism. With the help of this reactant, it was possible to establish the nature and mechanism of formation of intermediate short-lived radicals in photochemical process using ESR spectra of stable ARs. 

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