Ring with simultaneous

The parent compound and a set of monosubstituted bis(acylamino)diarylspiro-X4-sulfanes (360 X = H, Me, MeO, Cl, NO2) undergo hydrolysis to the corresponding sulfoxides (361). The probable mechanism involves rate-determining cleavage of one of the S—N hypervalent bonds in the spiro ring with simultaneous proton transfer to the nitrogen atom. The hydroxide ion which is formed thereby then attacks the sulfur atom in a fast step to form a diaryl(acylamino)hydroxy-k4-sulfane (362), which is converted into the sulfoxide (361) (Scheme 47). ... 

Another interesting reaction of benzoxazines 114 (115) is the reductive opening of the oxazine ring with simultaneous dehydrogenation of the pyrazoline moiety [170]. This process is carried out in a KOH suspension of a mixture of dimethyl sulfoxide and dimethylformamide. For instance, this treatment involving 2,5-diary l-l,10b-dihydro-177-pyrazolo[l,5-c]benzo[e]-l,3-oxazines 116 leads to the formation of pyrazoles 117 (Scheme 2.32). Similar disproportionation reactions have also been described for some bezopiranes, for example, pyrazole derivative 118 [91, 170]. 

Nitration of triazolinones (possibly reacting as phenolic hydroxytriazoles) with fuming nitric acid affects the heterocyclic ring with simultaneous nitration of the benzene ring in 1- and 4-phenyl derivatives. However, 2- or 3-phenyl derivatives of l,2,4-triazolin-5-one are nitrated in the benzene ring exclusively (69cb75s). 

Free forms of the vitamin are white, stable solids that are quite soluble in water. The oxidized coenzymes are labile to alkali, whereas the reduced (dihydro) coenzymes are labile to acid. Reduction of the oxidized coenzymes commonly occurs by addition of a hydride ion to the para (4) position of the nicotinamide ring, with simultaneous formation of a solvated proton. NADH and NADPH (but not NAD and NADP) absorb light in the near ultraviolet region (339 nm). This forms the basis for many biochemical assays. 

Treatment of 5,5-dimethyl-e /o-4,6-diphenyltricyclo[4.1.0.0 ]heptan-2-one (36) with lithium aluminum hydride in refluxing tetrahydrofuran cleaved the cyclopropane ring with simultaneous reduction of the carbonyl group and produced the substituted en fo-bicyclo[2.2.1]heptan-2-ol 37 in good yield. 

Addition polycondensations may occur through addition of functional groups onto a double bond or by addition onto heterocyclic rings with simultaneous ring opening. Polyurethane formation from diols and... 

In another interesting application of this procedure, the acid-mediated cascade cyclization of (3-diketone diepoxide 73 involves the participation not only of the two oxirane rings and of the secondary alcoholic group, but also of one of the two carbonyl groups. In this way, besides the two adjacent C and D THF rings, the simultaneous construction of the spiroketal function between the B and C rings of etheromycin is obtained (compound 74, in a 70 30 mixture with 12 -epi compound Scheme 8.19) [37]. 

From 95 g of SOCI2 and 183 g of H2S , both dissolved in CS2 and added simultaneously but slowly (within 8 h) to a mixture of 0.75 1 CS2 and 0.35 1 Me20, ca. 4 g of pure SgO were obtained after repeated recrystallization. SgO forms needle-shaped yellow crystals of m.p. 78 °C (dec.). The molecules consists of a crown-shaped Sg rings with exocyclic oxygen atoms in axial positions [89]. 

The amine opens the THF ring system because of a nucleophilic attack at the a-C atom of the coordinated THF. Owing to the movement of a proton from the ethyl to the amide group with simultaneous ethene elimination, a betaine structure appears. 

An example, where two C-C-bonds are formed and one C-C-bond is broken is the synthesis of the tricycle 3-285, which has some similarity with the eudesmane framework 3-286, developed by Kilburn and coworkers (Scheme 3.72) [113]. Thus, exposure of the easily accessible methylenecyclopropyl-cyclohexanone 3-281 to samarium(II) iodide led to the generation of ketyl radical 3-282, which builds up a six-membered ring system with simultaneous opening of the cyclopropane moiety. Subsequent capture of the formed radical 3-283 by the adjacent alkyne group afforded the tricycle 3-285 via 3-284 as a single diastereoisomer in up to 60% yield. It should be noted that in this case the usual necessary addition of HMPA could be omitted. 

Clayden and co-workers reported the dearomatiztion of an electron-deficient pyridine ring via intramolecular cyclization of an enolate shown in the scheme above <06OL5325>. Generation of the amino acid derived enolate of 46, with simultaneous activation of the pyridine ring by IV-acylation, leads to a stereoselective transition state 47. The authors postulate that the stereoselectivity arises from the manner in which the bulky PMP (p-... 

Alkenyl Fischer carbene complexes can serve as three-carbon components in the [6 + 3]-reactions of vinylchro-mium carbenes and fulvenes (Equations (23)—(25)), providing rapid access to indanone and indene structures.132 This reaction tolerates substitution of the fulvene, but the carbene complex requires extended conjugation to a carbonyl or aromatic ring. This reaction is proposed to be initiated by 1,2-addition of the electron-rich fulvene to the chromium carbene followed by a 1,2-shift of the chromium with simultaneous ring closure. Reductive elimination of the chromium metal and elimination/isomerization gives the products (Scheme 41). 

While the notion that the alkoxides derived from aliphatic alcohols are poor nucleophiles toward 7r-allylmetal complexes has prevailed over the years, much progress made in the recent past has rendered the transition metal-catalyzed allylic alkylation a powerful method for the O-allylation of aliphatic alcohols. In particular, owing to the facility of five- and six-membered ring formation, this process has found extensive utility in the synthesis of tetrahydrofurans (THFs) (Equation (29))150-156 and tetrahydropyrans (THPs).157-159 Of note was the simultaneous formation of two THP rings with high diastereoselectivity via a Pd-catalyzed double allylic etherification using 35 in a bidirectional synthetic approach to halichondrin B (Equation (30)).157 The related ligand 36 was used in the enantioselective cyclization of a Baylis-Hillman adduct with a primary alcohol (Equation (31)).159... 

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