Complexes reaction with oxetanes

Carbonylcarbene reacts with oxetane in a complex manner, giving cyclopropane and propene by a deoxygenation process and ketene plus ethylene as apparent insertion-fragmentation products (equation 66). The reaction is carried out by irradiation of a solution of carbon suboxide in oxetane under these conditions, photodecomposition of intermediates is possible. The initial attack is believed to be at the ring oxygen atom to give a zwitterionic species (78JA6425). 

A few years later, Baba reported a more comprehensive description of the coupling reaction of oxetane and C02 catalyzed by organotin iodides and Lewis bases as catalysts [60]. It was shown in this instance, that the choice of Lewis base which coordinated to the organotin iodides affected the catalytic activity and selectivity, that is, poly(TMC) and/or trimethylene carbonate. Whilst complexes with Bu3P yielded polycarbonate, the combination of Bu3SnI with Bu3P=0 yielded TMC exclusively in good yields. A reaction mechanism, as proposed by Baba and coworkers, is illustrated in Scheme 8.5. 

Isatine derivatives gave the corresponding cycloadducts with high stereoselectivity when irradiated in the presence of furan and benzofuran [72]. The reaction of furan with acyl cyanides yields the corresponding oxetanes, but both diastereoisomeric endo- and exo-oxetanes are formed (Scheme 3.36). When chiral acyl cyanides are used, low asymmetric induction is observed [73]. Furan also reacts with chiral ketones. In this case, an ot-cleavage reaction before the 2+2 cycloaddition modifies the expected products (Scheme 3.37). When (—)-menthone was used as a substrate, a chiral product was obtained as a 2 1 diastereoisomeric mixture the most abundant product has the (1/ , 3R) configuration [74]. When the reaction was performed on carbohydrate 36, a complex reaction mixture was obtained (Scheme 3.38) [74, 75]. 

To make ethers more reactive, they must be complexed with strong Lewis acids. BF3 is commonly used with cyclic ethers, and even with epoxides it increases the rate and yield of the reaction when organometallic reagents are used as nucleophiles. BF3 is most easily handled as its complex with diethyl ether, written BF3 OEt, BuLi does not react with oxetane, for example, unless a Lewis acid, such as BF3, is added, when it opens the fouremembered ring to give a quantitative yield of H-heptanoI. 

Baba, A., Kashiwagi, H., Matsuda, H., 1987. Reaction of carbon dioxide with oxetane catalyzed by organotin halide complexes control of reaction by ligands. Organometallics 6, 137-140. 

Z. Chen, B. Wang, Z. Wang, G. Zhu, J. Sun, Angew. Chem. Int. Ed. 2013, 52, 2027-2031. Complex bioactive alkaloid-type polycycles through efficient catalytic asymmetric multicomponent aza-Diels-Alder reaction of indoles with oxetane as directing group. 

Reactions with Oxiranes, Oxetanes, and Aziridines. Lewis acids, lanthanide salts, and titanium tetraisopropoxide or aluminum isopropoxide catalyze the reactions of cyanotri-methylsilane with oxiranes, oxetanes, and aziridines, yielding ring-opened products. The nature of the products and the regio-selectivity of the reaction are primarily dependent on the nature of the Lewis acid, the substitution pattern in the substrate, and the reaction conditions. Monosubstituted oxiranes undergo regiospe-cific cleavage to form 3-(trimethylsiloxy)nitriles when refluxed with a slight excess of cyanotrimethylsilane in the presence of a catalytic amount of potassium cyanide-18-crown-6 complex (eqs 8-10). The addition of cyanide occurs exclusively at the least-substituted carbon. 

The Patterno-Buchi coupling of various stilbenes (S) with chloroanil (Q) to yield fran -oxetanes is achieved by the specific charge-transfer photo-activation of the electron donor-acceptor complexes (SQ). Time-resolved spectroscopy revealed the (singlet) ion-radical pair[S+% Q" ] to be the primary reaction intermediate and established the electron-transfer pathway for this Patterno-Buchi transformation. Carbonyl quinone activation leads to the same oxetane products with identical isomer ratios. Thus, an analogous mechanism is applied which includes an initial transfer quenching of the photo-activated (triplet) quinone acceptor by the stilbene donors resulting in triplet ion-radical pairs. ... 

These l-hydroxy-2-metalla (5,6,7)-allyl complexes result directly from the reactions of the less sterically crowded complexes [lr(Cn)(cod)](OTf) (Cn = 1,4,7-triazacyclononane) [82] and [Rh(/c -Py3S3)(cod)](BPh4) [81]. Slowing down the reactions by increasing the steric crowding around the metal, the kinetic isomers 2-irida oxetane and 6,7-oxarhoda tetracyclodecane can be isolated from the reactions of [lr(Cn )(cod)](OTf) [82] and [Rh(/c -L )(cod)](Pp6) (L = Cn, dpa-R ) [72,79] with H2O2, respectively. The... 

The mechanism of decarboxylation of /3-lactones has attracted much attention. The gas-phase decomposition of 2-oxetanone is a unimolecular first-order process. It has a considerably lower energy of activation than the pyrolysis of oxetane and a much higher entropy of activation, indicating a loose activated complex (69JA7743). The ease of the reaction is greatly affected by the electronic effect of substituents at position-4, but not at position-3. The Hammett treatment of a series of rrans-4-aryl-3-methyl-2-oxetanones gave a good correlation with [Pg.374]

Oxetane formation is presumed to occur via the singlet exciplex however, excitation of the ground state charge-transfer complex may be necessary in order for the formation of 39 to compete with the rapid isomerization of c-1. The factors which favor oxetane versus cyclobutane formation in this reaction are not understood. 

The reaction of 3-phenyloxetane (10) with nitric acid in dichloromethane and trichloromethane under anhydrous conditions has been investigated.35 Quantitative conversion into 2-(nitrophenyl)propane-l,3-diol dinitrates occurs. The substrate reacts through its majority hydrogen-bonded complexed form initially by a mixture of aromatic nitration and oxetane ring opening. The nitration, perhaps surprisingly, proceeds at a rate comparable to that of / -dichlorobenzene. 

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