Oxaspiro compounds

Rearrangements of oxaspiro compounds such as l,5-dioxaspiro-(2,6) octane and... 

The allenic ether (204) cyclizes to spiro compounds in the presence of potassium r-butoxide and dicyclohexano-18-crown-6. Acid hydrolysis yields the dihydrofuranone (205). The new carbonyl compound l-oxaspiro[4,4]nonan-4-one can be subjected to another spiroannela-tion sequence. The carbonyl group in (206) has two faces available for addition of a nucleophilic species. Only one product is formed, a cyclopentyl[3]helixane (207). One can in principle continue this reiterative reaction (Scheme 53) (B-81MI31200). 

A severe limitation of this method, however, is the failure of the ylide 103 to yield oxaspiropentanes vide supra) from a,p-unsaturated ketones and the poor yields of vinylcyclopropanes obtained from its reactions with hindered ketones or with con-formationally rigid six-membered rings. Moreover, attempts to extend the oxaspiro-pentane ring opening to compounds containing an adjacent tertiary center have failed thus, oxaspiropentane 110 did not lead to 111, Eq. (33) 57). 

Among the systems with chemical different donor and acceptor molecules, the photocopolymerization between maleic anhydride (MSA), which functions as an acceptor, and electron-rich monomers has been widely investigated. As donor monomers such compounds as styrene (Sty) [19-29], cyclohexene [30], N-vinylcarbazole [31], 2-vinyl naphthalene [32], vinyl acetate [33], 2.4.8.10-tetra-oxaspiro[5.5]undecan [34] and phenyl glycidyl ether (2,3-epoxypropyl phenyl ether, PGE) [35] have been used. In all the above cases, using high concentrations of both monomers, the absorption of the CT has been obtained in various solvents. Thus, with spectroscopic methods the complex formation constant Kct can be calculated (e.g., MSA-cyclohexene Kcl = 0.0681 mol -1 [33], MSA-tetrahydrofuran Kct = 0.331 mol-1 [36]), and a selective excitation of the CT is possible in many cases. 

The ozonation of Feist s ester yields three products 2,3-dicarbomethoxytetrahydrofuran-4-one (III), 3,4-dicarbome-thoxy-5-hydroxy-2-oxa-2,3-dihydropyran (IV), and 4,5-di-carbomethoxy-l-oxaspiro[2.2 pentane (V). Structures were assigned primarily through spectroscopic evidence (mass, NMR, and infrared spectra). The last of these compounds is probably not a direct ozonation product (stoichiometry and trapping studies). A mechanism is proposed in which the initial step is formation of a primary ozonide. From that stage, the breakdown is abnormal. 

Finally, the oopolymerization of a compound with two oxetano rings with another appropriate difunctional oompound has been used. Examples cited here are the reactions of. 2,6- oxaspiro[3.3]heptane with phthalic anhydride s with terphthaloyl chloride The latter polymer appeared to be croeslinkcd as it was insoluble in all solvents tosted and contained considerably less than the theomtjoaj amount of chlorine. 

The wide applicability of the cyclopropanation reaction allows the preparation of intermediates for elaborated compounds. The preparation of trans- and cw-l-phosphoryl-5-oxo-4-oxaspiro[2.3]hexanes 1, which are important intermediates for the synthesis of heterocycles or functionalized cyclopenten-l-ones, illustrates well the potential of this reaction. 

In contrast to methylenecyclopropane, bicyclopropylidene reacted with singlet oxygen generated photochemically. The reaction products were 7-oxadispiro[2.0.2.1]heptane and spiro[2.3]hexan-4-one (ratio 10 6). Both compounds were also obtained by reacting ozone with bicyclopropylidene, together with a third product, which was identified as 7-oxaspiro-[2.4]heptan-4-one (relative amount 67%). °... 

Generation of a cyclopropyl enolate 4 in situ was reported on reaction of 6-cyclopropylidene-5-oxaspiro[2.3]hexan-4-one (3) in dichloromethane at room temperature with nucleophiles such as alcohols, phenols, fluoride, and enamines. The enolate 4 was subsequently treated with an electrophile, such as a proton, iminium salt or carbonyl compound. " ... 

Dimethoxy-l,l-dimethyl-4-oxaspiro[2.3]hexane (3) can be hydrolyzed into the functionalized cyclopropanol 4 or dimerized into the eight-membered-ring compound 5. The latter could also be hydrolyzed into cyclopropanol 4 in 84% yield. 

Dry glycerol (5.53 g, 60 mmol) and dibutyltin oxide (14.94 g, 60 mmol) in 120 mL of toluene were refluxed for 4 h under argon. The theoretical amount of water was collected in a Dean-Stark sidearm. The reaction mixture was cooled to 70 C and 4-chloromethyl-l,3-dioxolane-2-thione (5 9.16 g, 60 mmol) (7) was added to the cyclic tin compound 4 in one portion. After 5 h, the solvent was removed under reduced pressure to leave a two-phase liquid residue. The dibutyltin sulfide by-product was removed by several extractions with hexane to provide the crude chloromethyl-hydroxy-substituted oxaspiro intermediate 6 as a pale yellow oil in 99% yield. 

HPLC fractionation of a SOCM sample into its individual components provided information about the relative proportions of the various isomers. The ratio of 3a to 3b was approximately 3 1 as determined by peak areas (UV detection at 254 nm) of the HPLC chromatograms. This should be a reasonably good estimation of product ratio since the pendant methacrylate functionality is the only UV active group in these compounds. Die spiro-fused five-membered rings were characterized by a CO4 resonance at 135 ppm in the C NMR spectra. By contrast, the compounds of type 3b, with mixed five- and six-membered ring sizes, produced CO4 signals at 122 ppm. A small amount of an oxaspiro dimethacrylate (8, Figure 7) was also noted. This... 

Another compound, DDFB, was also investigated to determine its potential as a dual radical/cationic polymerization initiator with the SOCM monomer. The dark DDFB solid had only limited solubility in the monomer (approximately 0.5 wt%). The activated SOCM sample was heated to 100 C for 10 min which produced a darkened polymer that was predominantly crosslinked. An unactivated SOCM control sample also received the same heat treatment and was recovered unchanged. The IR spectrum of the polymer showed extensive carbonate formation in the 1800 and 1750 cm regions and a nearly complete disappearance of the spiro absorption bands. This initiator appeared to have little affinity for the methacrylate double bond since a strong 1637 cm band was still present. The attempted polymerization of oxaspiro monomer 10 with DDFB at 100 C yielded no polymer and no reaction. The DDFB-containing SOCM monomer sample was then irradiated under the sunlamp with no polymer formation observed after 30 min. 

The reaction of geminal dibromides and carbonyl compounds in the presence of butyl-lithium or lithium metal can provide a general route to a wide range of oxirans. Stevens and Pillai have used a Darzens cyclization reaction to form the first example of an isolable epoxy-amine (121). 2-(l-Aziridinyl)-2-phenyl-l-oxaspiro[2,5]octane (121) was relatively stable and rearranged to the corresponding cycloheptanone (122) only after... 

Formation of Aminotetrahydrofuran Derivatives 3-7 from Complexes 3-2 and Ketones. A General Procedure for Preparation of ((Z)-(( )-2-Amino-2-Schlenk tube, a ketone (0.5 mmol, 1.0 eq.) was added to the benzene solution (3 mL) of compound 3-2 (318 mg for 3-2a, 337 mg for 3-2b, 0.5 mmol). After the reaction mixture was stirred at 90 °C for 1 h, the reaction mixture was quenched with saturated aqueous NaHCOs. The resulting mixture was extracted with diethyl ether for three times and then washed with water and brine. The extract was dried over anhydrous MgS04. The solvent was evaporated in vacuo to give a yellow solid, which was subjected to Si02 column using petroleum ether, diethyl ether, and triethylamine (100 15 1) as the eluent to give product 3-7a. 

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