Synthesis and Photochemistry of 5,5-Dimethyl-1H-pyrrol-2(5H)-one and of Some N-Substituted Derivatives

In two steps, 5,5-dimethyl-1H-pyrrol-2(5H)-one ( 3a ) was prepared from 5,5-dimethylpyrrolidine-2,4-dione ( = dimethyltetramic acid; 4 ) in 71% overall yield (Scheme 1) and further converted to N-substituted derivatives 3b–f via acylation, alkylation, or methoxycarbonylation of its anion (Scheme 2). The substituents on the N-atom exert a strong influence on the photochemical reactivity ([2 + 2] photocycloaddition to 2,3-dimethylbut-2-ene, photocyclodimerisation, photoreduction) of these aza-enones 3 (Scheme 3). In general, N-alkyl compounds react much slower and with less efficiency than either the (N-unsubstituted) title compound 3a or its N-acetyl and N-(methoxycarbonyl) derivatives 3e and 3f , respectively. These compounds behave similarly to the corresponding lactone, 5,5-dimethyl-2(5H)-furanone, studied previously.     

The Photochemical Behaviour of 5,5-Dimethyl-2(5H)-furanone

The photochemical behaviour of the title compound 2c was investigated in various solvents. In benzene and t-butanol photodimerization affords the cis-anti-cis HH- and HT-dimers (H = head, T = tail). In acetonitrile, cyclohexane and 2-propanol, photoreduction competes with photodimerization. The photoreduction products are hydrodimers, solvent adducts and the saturated lactone (the 2H-reduction product). In acetonitrile and cyclohexane H-abstraction by the β-C-atom of the C?C bond is the predominant reduction process. In 2-propanol, solvent adducts to the α- and β-C-atoms are formed in equal amounts. In xanthone-sensitized irradiations the ratio of HH- to HT-dimer is the same as on direct irradiation and the relative rates of conversion of 2c to products in different solvents are also similar under both conditions.     

Synthesis and Photochemistry of 2,2-Dimethyl-3(2H)-thiophenone,a Ketonic Tautomer of 3-Hydroxythiophene. Preliminary Communication

On irradiation (λ = 366 nm), the 4-thia-2-cyclopentenone 3a behaves in complete analogy to the oxa-enone 3c undergoing regio- and stereospecific cyclodimerization, regiospecific cycloaddition with 2-methylpropene and cycloaddition with 2,3-dimethyl-2-butene to afford cyclobutane derivatives. In contrast, the 4 -aza-2-cyclopentenone 3b does not undergo the above-mentioned reactions but only slow photodecomposition.     

Photochemistry of 2,2-Dimethyl-2H-Furo[3,4-b]Pyran-4,7(3H, 5H)-Dione

Irradiation (λ > 340 nm) of the title compound 2a in t-BuOH affords 3,3,10,10-tetramethyl-2,8-dioxatricyclo-[4.3.2.0^1,6]undecane-5,9-dione (3) via photoextrusion of 2-methylpropene and subsequent photocycloaddition of 2a to the alkene. The same regioisomer 3 is formed selectively and in much higher yields on irradiating 2a in the presence of excess 2-methylpropene. Irradiation of 3 (λ = 300 nm) in t-BuOH in the presence of the same alkene gives a 6:1 mixture of spirooxetanes 7a and 7b but not α-cleavage products. In 2-propanol, 2a is photoreduced to a 2:1 mixture of diastereoisomeric hydrodimers 9 .     

Photochemistry of Thiophen-2(5H)-ones

Mechanistic evidence for the light-induced ring opening of thiophen-2(5H)-ones 1 in alcohols affording α, β-unsaturated mercapto esters 2 is presented. Regio-and stereochemical aspects of the ring closure of alkenylthio (type 3 ) radicals 15 and 17 to S-heterocycles 16 and 18 , of 3-thiahex-5-enyl radicals 4 to (tetrahydrothien-3-yl)methyl radicals 6 and of (2,3-dihydrothien-3-yl)methyl radicals 30 (type 7, but-3-enyl radicals) to cyclopropane-methyl radicals 29 are discussed. Irradiation (λ 350 nm) of 1 in cyclohexane in the presence of 2,3-dimethylbut-2-ene affords [2 + 2] cycloadducts 14 albeit in very low yields.     

Photochemistry of water: the (H2O)5 cluster

The structures of the cyclic water pentamer, the H3O+(H2O)3OH- zwitterion, and the H3O(H2O)3OH biradical form of the (H2O)5 cluster have been determined with the second-order M?ller-Plesset method and with density-functional theory (DFT). The vertical singlet excitation energies of these structures have been calculated with the second-order approximated coupled-cluster method and with time-dependent DFT, respectively. The molecular and electronic structures of the H3O(H2O)3OH biradical have been characterized for the first time. The lowest electronic states of the biradical are slightly lower in energy than the vertically excited states of the covalent and zwitterionic (H2O)5 clusters and therefore are photochemically accessible from the latter. The electronic absorption spectrum of the biradical exhibits the characteristic features of the absorption spectrum of the hydrated electron. It is argued that the basic mechanisms of the photochemistry of water, in particular the generation of the hydrated electron by UV photons, can be unraveled by relatively straightforward electronic structure and dynamics calculations for finite-size water clusters.     

(4R)-5,5-二甲基-4-苄硫甲基-2-噁唑烷酮的合成

以价廉易得的天然L-半胱氨酸为原料,经巯基保护、酯化、氨基保护、格氏反应及环化等5步反应,合成了一个新的手性助剂(4R)-5,5-二甲基-4-苄硫甲基-2-噁唑烷酮,总收率31%.产物结构经IR,~1H NMR,~(13)C NMR及MS表征.     

Photochemistry of 6,6-Dimethyl- and 2,2,6,6-Tetramethyl-2H,6H-pyran-3-one

The title compounds 1a and 1b have been synthesized in two steps from the saturated pyran-3-ones 2a and 2b , respectively. Upon irradiation (254 nm or 350 nm) in dilute solutions (10^?3?10^?2M ), compounds 1 undergo a formal [4 + 2] cycloreversion from the excited triplet state to give (2-methylprop-1-enyl)ketene ( 11 ) and either formaldehyde or acetone, ketene 11 being trapped by H₂O or MeOH to afford 4-methylpent-3-enoic acid ( 5 ) or its methyl ester 4 in 75–85% isolated yield. In this (monomolecular) photoreaction, heterocycles 1 differ from their alicyclic counterparts, i.e., 4,4-dimethylcyclohex-2-enone ( 10a ) and 4,4,6,6-tetramethylcyclohex-2-enone ( 10b ), as no rearrangement to a 4-oxabicyclo[3.1.0]hexan-2-one occurs. On the other hand, the photochemical behavior of pyranone 1a in bimolecular reactions (cyclodimerization, [2 + 2] cycloaddition to 2,3-dimethylbut-2-ene) resembles that of enone 10a .     

Photochemistry of N-aryl-2(1H)-pyrimidin-2-ones

Irradiation of N-aryl-2(1H)-pyrimidin-2-ones ($\text{3a}$-$\text{c}$) in a mixed benzene-alcohol solution afforded the products initiated by Type I cleavage, 1-(3-alkoxycarbonylamino-2-propene)-N-arylimines ($\text{4a}$-$\text{c}$, $\text{5}$, and $\text{6}$) in 45–51% yields.     

Stereoselective Synthesis of 2-Chloro-4-Substituted-phenyl-5,5-Dimethyl-1,3,2-Dioxaphosphorinan-2-(Thi)ones

1,3,2-DioxaPhoSPhorinaneringsystemhasbeenasubjectofconsiderableinterestformanyyearsbecauseofitSdiversebiologicalachvitieSIl'21andcomPlicatedstereocheAnstryl"'].AsacontinuationofourinterestinthesynthesisandstereochendstryoncycliCPhosPhoruscomPoundsl"'l,wewouldlilietorePOrthereinthestereoselechvesynthesisof2-chloro-4-subshtUted-phenyl-5,5-ddriethyl-l,3,2-dioxaPhoSPhorinan-2-(thi)ones,whicharethekeyintermediatesforthesynthesesofl,3,2-dioxaPhoSPhohaanederivatives.Generallyspeaking,2-chloro…     

N-(5,5-二甲基-1,3,2-二氧杂己内磷酰基)取代苯甲醛腙的合成及其阻燃性能

环状磷酸酯;水合肼;膨胀型阻燃剂;N-(5;5-二甲基-1;3;2-二氧杂己内磷酰基)取代苯甲醛腙的合成及其阻燃性能     

5,5-二甲基-2-磷杂-1,3-二噁烷-2-基烯丙基磷酸酯的制备

以新戊二醇、三氯氧磷、烯丙醇和金属钠为原料,经过2步反应合成了新型反应型阻燃化合物5,5-二甲基-2-磷杂-1,3-二噁烷-2-基烯丙基磷酸酯。 采用元素分析、FTIR、MS和1H NMR等测试技术对其结构进行了表征。 对合成工艺进行了探讨,当n（Na）∶n（烯丙醇）=1∶2,于冰水浴反应2 h,再于30 ℃反应6 h时,产率可达55.5%。 TG分析显示,该化合物的起始分解温度为130.2 ℃,800 ℃时仍有23%的残炭率,说明该化合物具有较好的热稳定性和成炭性。     

Molecular and crystal structure of 2-(N-benzyl-N-phenylhydrazinoethylidene)-3-(2H)-benzo[b]-thiophenone

X-ray structural analysis was used to determine the molecular and crystal structure of 2-(N-benzyl-N-phenylhydrazinoethylidene)-3-(2H)-benzo[b]thiophenone. The crystals are monoclinic, the space group isC2/c,a=16.022(6),b=11.202(3),c=22.111(4) Å, =81.08(3)°, and andZ=8. It was shown that the ability of hydrazones of a similar class to exhibit photochromic properties is a function of the steric stresses in the molecules and their confirmation.Institute of Chemical Physics in Chernogolovka, Russian Academy of Sciences, 142432 Chernogolovka. Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 12, pp. 2805–2809, December, 1992.