Intramolecular addition reactions methanol

Discrete dimers of the head-to-head type have been found in the structures of the Ag+ complex of (145)570 and the Na+ complex of (145)571 respectively. The complexes were recrystallized from carbon tetrachloride. In both complexes each metal is five-coordinated in the cavity provided by one anion, and there is an additional reaction with the second anion [through an Ag+-phenyl interaction or an Na+-carboxylate oxygen atom (Figure 32a)]. When the Na+ complex was crystallized from a solvent of medium polarity, acetone, the head-to-head dimer was recovered.571 In contrast, recrystallization from a polar medium, methanol, gave a monomeric complex in which one methanol of solvation was also present.572 In all of these complexes an intramolecular head-to-tail hydrogen bond was present to hold the ligand in its pseudo-macrocyclic conformation. 

Analysis of the product distributions arising from both sensitized and non-sensitized irradiation of 2-allyloxyphenyldiazo species (8) showed that the C—H insertion product and much of the cyclopropanation arise from the triplet carbene.16 For the singlet carbene, intermolecular 0—H insertion with methanol is about 50 tunes faster than intramolecular addition to the double bond, hi this system, intramolecular reactions and intersystem crossing of the triplet carbene proceed at similar rates, hi the closely related indanyl system (9), the smaller RCR angle stabilizes the singlet state relative to the triplet and the intramolecular reactivity is dominated by the singlet state.17... 

The rate and the conversion of the Baylis-Hillman-reaction was significantly improved when nucleophilic non-hindered bases, such as diaza[2.2.2]bicyclooctane (DABCO, 6), rather than simple tertiary amines were used. Further improvements were observed when 3-quinuclidinole (3-QDL, 7) was employed, due to stabilization of the zwitterionic intermediate 2 by formation of intramolecular hydrogen bonds [14a-c]. Similar effects were observed by the addition of methanol [14d] or acetic acid [14e] to the reaction mixture (formation of intermolecular hydrogen bonds) or by the presence of a hydroxy group in the acrylate [14f ]. The rate of the reaction was decreased by the presence of substituents in the a-position of tertiary amines. This was explained by the decrease of the rate of the addition of the catalyst onto the acrylate [15]. 

This type of reaction has some precedence i.e., cyanohydrin formation (KCN, DMSO), followed by intramolecular displacement of a tosylate by the incipient alkoxide leads to the formation of a 2-cyano oxetane system. Furthermore, KCN in MeOH results in the addition of methanol across a nitrile group. Nerdel, F. Weyerstahl, P. Lucas, K. Tetrahedron Lett. 1965, 5751. 

The reaction has also been carried out under alkaline conditions, with hydroxide in aqueous dioxane. The mechanism here involves nucleophilic attack by hydroxide at the carbon atom. An intramolecular addition of an alkyne (in an ortho alky-nyl phenyl isonitrile) to the carbon of an isonitrile occurred with heating in methanol to give quinoline derivatives. ... 

Furanophane 155 adds singlet oxygen and undergoes an intramolecular addition giving 178 if the reaction is conducted in methanol,288 but in dichloromethane two oxygen molecules add and the product (179), being intrinsically unstable, rearranges to the remarkable polyepoxide (180).289... 

Intramolecular Additions - The truxinic acid derivative (23) is formed on irradiation of (24) in methanol using a Pyrex filter. The reaction is quantitative and has a quantum yield of 0.55. Similar reactivity is observed when crystals of (24) are irradiated. The use of a benzene ring as a constraint has provided a method for the formation of a single stereoisomer in high yield this is seen best of all with the yield this is cinnamate ester (25). Irradiation of (25) for 21 h in methylene chloride solution affords an 88% yield of (26). A less efficient reaction... 

Periana et al. have reported a mercury system that catalyzes the partial oxidation of methane to methanol.81 Hg(II) is typically considered to be a soft electrophile and is known to initiate electrophilic substitution of protons from aromatic substrates. The catalytic reaction employs mercuric triflate in sulfuric acid, and a key step in the catalytic cycle is Hg(II)-mediated methane C—H activation. For methane C—H activation by Hg(II), an oxidative addition reaction pathway via the formation of Hg(IV) is unlikely. Thus, an electrophilic substitution pathway has been proposed, although differentiation between proton transfer to an uncoordinated anion versus intramolecular proton transfer to a coordinated anion (i.e., o-bond metathesis) has not been established. Hg(II)-based methane C H activation was confirmed by the observation of H/D exchange between CH4 and D2S04 (Equation 11.9). 

Intramolecular Additions to Cyclopentenones - Irradiation (k > 350 nm in THF) of the enone (46) affords a single diastereoisomer identified as (47, 95%). The outcome of the reaction does not seem to be solvent dependent and the same degree of success is obtained with methylene chloride, acetonitrile or methanol as solvents. The corresponding amide also cyclizes efficiently. Crimmins and coworkers have demonstrated that irradiation (X > 350 nm) of the enone (48) results in cycloaddition and the formation of the diastereoisomeric adducts (49) and (50) in a ratio of 83 17. A single product (51) is obtained on irradiation of the related enone (52). These adducts are key intermediates in a synthesis of some spirovetivanes. 

Some attempts to use aliphatic alcohols as nucleophiles in the enantioselec-tive conjugate addition to enals have been carried out, but with no success with regard to the stereochemical control (Scheme 3.29). For example, the conjugate addition of methanol to several aliphatic enals using axially chiral amines derived from BINOL as catalysts proceeded with enantioselectivities around 50% ee and also a 31c-catalyzed intramolecular reaction leading to the formation of the tetrahydropyrane skeleton has been reported to proceed with 57% ee. 

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