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1.
[reaction: see text] A new Prins-type cyclization between homopropargylic alcohol and aldehydes in the presence of FeX(3) to obtain 2-alkyl-4-halo-5,6-dihydro-2H-pyrans in good yield is described. Osmium-catalyzed cis dihydroxylation provided direct access to trans-2-alkyl-3-hydroxy-tetrahydro-pyran-4-ones. Anhydrous ferric halides are also shown to be excellent catalysts for the standard Prins cyclization using homoallylic alcohol. Isolation of an intermediate acetal provides substantiation of a proposed mechanism.  相似文献   

2.
Iron(III) halides have proven to be excellent catalysts in the coupling of acetylenes and aldehydes. When terminal acetylenes were used the main products obtained were 1,5-dihalo-1,4-dienes with (E,Z)-stereochemistry contaminated in some cases with (E)-alpha,beta-unsaturated ketones. The former carbonyl derivatives were the sole products isolated when nonterminal aromatic alkynes were used. When homopropargylic alcohols were used, a Prins-type cyclization occurred yielding 2-alkyl-4-halo-5,6-dihydro-2H-pyrans. In addition, anhydrous ferric halides are also shown to be excellent catalysts for the standard Prins cyclization with homoallylic alcohols. Isolation of an intermediate acetal, calculations, and alkyne hydration studies provide substantiation of a proposed mechanism.  相似文献   

3.
The reaction of 4-alkyl-4-hydroxy-2-alkynenitriles with hydrogen halides (HCl and HI) in dioxane is accompanied by intramolecular cyclization with formation of 5,5-dialkyl-4-halo-2-imino-2,5-dihydrofuran hydrohalides. Treatment of the latter with K2CO3 in ethanol yields 5,5-dialkyl-4-halo-2-imino-2,5-dihydrofurans.  相似文献   

4.
The reaction of 3-azido-2,3-dideoxypyranose and 3-azido-2,3-dideoxy-2-halohexopyranose compounds with (diacetoxyiodo)benzene and iodine generated 2-azido-1,2-dideoxy-1-iodoalditols and 2-azido-1,2-dideoxy-1-halo-1-iodoalditols, respectively. These beta-iodo azides could be transformed by chemoselective dehydroiodination into 2-azido-1,2-dideoxy-4- O-formyl-pent-1-enitols and (Z, E)-2-azido-1,2-dideoxy-1-halo-4- O-formyl-pent-1-enitols in good yields. Thermolysis and photochemical studies of these vinyl azides and 1-halovinyl azides for the synthesis of polyhydroxylated 3-alkyl-2 H-azirines and the hitherto unknown 2-halo-3-alkyl-2 H-azirines have also been accomplished.  相似文献   

5.
An efficient synthesis of 2-alkyl-3-furoic acids has been developed. Addition of the lithium dianion of 4-oxo-2-phenylthiobutanoic acid ethylene acetal to aldehydes followed by acid-catalyzed cyclization produces furan products in high yield.  相似文献   

6.
1-Alkyl-5-halo-4-methoxypyridazin-6-ones were synthesized from 1-alkyl-4,5-dihalopyridazin-6-ones by the concurrent alkylation-methoxylation. 1-Alkyl-5-halo-4-hydroxypyridazin-6-ones were also prepared.  相似文献   

7.
Homoallylic alcohols (primary, secondary, or tertiary containing an endocyclic or an exocyclic double bond) react with equimolar amounts of aldehydes (aliphatic or aromatic) and ketones (aliphatic) in the presence of 5 mol % of iodine. This Prins cyclization was used in the preparation of hexahydrobenzo[f]isochromenes and of a 4-hydroxy-tetrahydropyran, in 54-81% yield. The procedure is also efficient for an aza-Prins cyclization of a homoallylic sulfonamide and benzaldehyde, producing a hexahydrobenzo[f]isoquinoline.  相似文献   

8.
An efficient alkene aza-Cope-Mannich cyclization between 2-hydroxy homoallyl tosylamine and aldehydes in the presence of iron(III) salts to obtain 3-alkyl-1-tosyl pyrrolidines in good yields is described. The process is based on the consecutive generation of a γ-unsaturated iminium ion, 2-azonia-[3,3]-sigmatropic rearrangement, and further intramolecular Mannich reaction. Iron(III) salts are also shown to be excellent catalysts for the new aza-Cope-Mannich cyclization using 2-hydroxy homopropargyl tosylamine.  相似文献   

9.
[formula: see text] Conrotatory ring closure of 1-halo-3-aza-4-alkyl-1,3-dienes in refluxing toluene gives rise to 3-halo-4-aryl-2-azetidinones in satisfactory yields. Dehalogenation of the resulting beta-lactams by tris(trimethylsilyl)silane furnished 3-unsubstituted azetidinones, valuable intermediates in the synthesis of biologically active compounds.  相似文献   

10.
Russian Chemical Bulletin - A method was developed for the synthesis of 4-alkyl-3,4-dihydronaphtho[2,3-f]quinoxaline-2,7,12-(1H)-triones starting from 1-chloroacetylamino-2-halo-9,10-anthraquinones...  相似文献   

11.
An intramolecular aza-Prins cyclization of aza-Achmatowicz rearrangement products was developed in which bismuth tribromide (BiBr3) plays a dual role as an efficient Lewis acid and source of the bromide nucleophile. This approach enables the facile construction of highly functionalized 9-azabicyclo[3.3.1]nonanes (9-ABNs), which are valuable synthetic building blocks and a powerful platform for the synthesis of a variety of alkaloid natural products and drug molecules. Suitable substrates for the aza-Prins cyclization include 1,1-disubstituted alkenes, 1,2-disubstituted alkenes, alkynes, and allenes, with good to excellent yields observed. Finally, we showcase the application of this new approach to the enantioselective total synthesis of six indole alkaloids: (−)-suaveoline ( 1 ), (−)-norsuaveoline ( 2 ), (−)-macrophylline ( 3 ), (+)-normacusine B ( 4 ), (+)-Na-methyl-16-epipericyclivine ( 5 ) and (+)-affinisine ( 6 ) in a total of 9–14 steps. This study significantly expands the synthetic utility of the aza-Achmatowicz rearrangement, and the strategy (aza-Achmatowicz/aza-Prins) is expected to be applicable to the total synthesis of other members of the big family of macroline and sarpagine indole alkaloids.  相似文献   

12.
Novel symmetrically and unsymmetrically disubstituted 1-azaadamantanes were prepared as a single, chiral diastereomer via double microwave-assisted aza-Prins cyclization in one-pot or sequential reaction format.  相似文献   

13.
A new general two-step methodology for the synthesis of chiral fluoro, chloro, bromo and iodo vinyl azides from carbohydrate-derived halohydrins has been developed. The anomeric alkoxyl radical fragmentation of 3-azido-2,3-dideoxy-2-halo-pyranoses under oxidative conditions with (diacetoxyiodo)benzene and iodine gave 2-azido-1,2-dideoxy-1-halo-1-iodo-alditols, which by chemoselective dehydroiodination afforded (Z,E)-2-azido-1,2-dideoxy-1-halo-4-O-formyl-pent-1-enitols in good overall yields. Preliminary thermolysis and photochemical studies of these compounds for the synthesis of hitherto unknown disubstituted 2-halo-3-alkyl-2H-azirines have also been accomplished.  相似文献   

14.
Novel pyridazino[4,5-b][1,4]oxazine-3,5-diones were synthesized from N-[2-(3,4-dimethoxyphenyl)-ethyl]-2-chloroacetamide (or 2-chloropropanamide) and 1-alkyl-5-halo-4-hydroxypyridazin-6-ones in good yield.  相似文献   

15.
Facile, versatile, and cost-effective synthetic routes for the preparation of a range of new 3-alkyl-, 4-alkyl-, 3,4-dialkyl-, and 3-halo-4-alkyl-2,2′-bipyrrole-5-carboxaldehydes have been developed. These 2,2′-bipyrrole-5-carboxaldehydes offer interesting potential as building blocks for making bioactive natural and unnatural products, as demonstrated by the synthesis of B-ring functionalized prodiginines (PGs) and tambjamines.  相似文献   

16.
In this full paper, a stereocontrolled strategy for the total synthesis of (?)-vindoline is described. This synthetic route features: 1) rapid construction of the stereochemical center at C19 through a highly diastereoselective vinylogous Mannich addition; 2) tandem Heathcock/aza-Prins cyclization to install rings C and E in vindoline; 3) oxidative transformation of β-ketoester to enone; 4) stereoselective inversion of C4 stereochemistry with triphenylphosphine and carbon tetrabromide followed by Brønsted acid.  相似文献   

17.
The radical cyclization reactions of unsaturated sulfonamides were investigated. The photolysis of N-(4-halo-4-pentenyl)sulfonamides (X=I, Br, or Cl) with (diacetoxyiodo)benzene (DIB) and iodine at room temperature afforded exclusively the corresponding piperidines in 73-98% yield via 6-endo radical cyclization. On the other hand, the reactions of N-(5-halo-4-pentenyl)sulfonamides with DIB/I2 led to the only formation of the pyrrolidine products in 84-99% yield via 5-exo radical cyclization. The vinylic halogen substitution not only successfully inhibits the competing ionic iodocyclization process to allow the radical cyclization to proceed smoothly but also shows a remarkable effect in controlling the regioselectivity of cyclization.  相似文献   

18.
Acid-catalyzed intramolecular addition of a hydroxy group to alpha-alkylated vinylsilanes has been studied. Treatment of (Z)-5-alkyl-5-silyl-4-penten-1-ols 1 (R = alkyl) with 5 mol % TiCl(4) in CHCl(3) gave trans-2-alkyl-3-silyltetrahydropyrans 2 exclusively (trans/cis = >99/1 to 97/3). The cyclization efficiency and rate strongly depended on the geometry of the C-C double bond and the silyl group. The use of (E)-vinylsilanes resulted in lower yields with poor cis-selectivity. In the cyclization of (Z)-1 (R = Bu), the silyl group used, the reaction time, and the yield of 2 were as follows: SiMe(2)Ph, 9.5 h, 75%; SiMe(3), 7.5 h, 66%; SiMePh(2), 24 h, 58%; SiMe(2)-t-Bu, 0.75 h, 85%; SiMe(2)Bn, 1.5 h, 78%. This 1,2-silyl-migrative cyclization could be applied to stereoselective synthesis of trisubstituted tetrahydropyrans. The acid-catalyzed reaction of 1-, 2-, or 3-substituted (Z)-5-silyl-4-nonen-1-ols 8 gave r-2,t-3,c-6-, r-2,t-3,t-5-, or r-2,t-3,c-4-trisubstituted tetrahydropyrans with high diastereoselectivity, respectively. (Z)-4-Alkyl-4-silyl-3-buten-1-ols 5 as well as 1 underwent the 1,2-silyl-migrative cyclization to give 2-alkyl-3-silyltetrahydrofurans 6 with high trans-selectivity. This silicon-directed cyclization was also available for the stereoselective synthesis of tri- and tetrasubstituted tetrahydrofurans.  相似文献   

19.
Cobalt/N-heterocyclic carbene system or cobalt/diamine combination effectively catalyzes sequential cyclization/cross-coupling reactions of 6-halo-1-hexene derivatives with trialkylsilylmethyl, 1-alkynyl, and aryl Grignard reagents. The sequential cyclization/cross-coupling reactions are applied to the synthesis of 1,3-diols starting from siloxy-tethered 6-halo-1-hexene derivatives.  相似文献   

20.
A novel C-thioacylation reaction is described. Reaction of aromatic or heterocyclic aldehydes with 1-alkyl-2-methyl-1,4,5,6-tetrahydropyrimidine or 1-alkyl-2-methylimidazolidine in the presence of sulphur leads to the thioacylketeneaminals 6, 10 or 12 in low to moderate yields. The structure of 6e was proved by S-methylation to 7e and acid-hydrolysis to the known 8e. Oxidative cyclization of 6 leads to the isothiazolo[2,3-a] pyrimidinium salts 13.  相似文献   

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