[4 + 2] Cycloadditions of a vinylketenimine. New route toward functionalized cyclohexenone derivatives (original) (raw)
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European Journal of Organic Chemistry, 2005
The bromination of 2-alkylidene-tetrahydrofurans and 2-alkylidene-pyrrolidines − readily available through one-pot [3+2] cyclization reactions − afforded 2-alkylidene-1Ј-bromotetrahydrofurans, 2-alkylidene-3-bromotetrahydrofurans and 2-alkylidene-1Ј,3-dibromotetrahydrofurans and their pyrrolidine counterparts. 2-Alkylidene-1Ј-bromotetrahydrofurans [a] 4815 were functionalized by performing Suzuki and Heck reactions. 2-Alkylidene-1Ј,3-dibromotetrahydrofurans were successfully employed in novel double-Suzuki reactions. (www.eurjoc.org Eur. J. Org. Chem. 2005, 4815-4828 4816 Scheme 4. Suzuki-reactions of 2-alkylidene-tetrahydrofurans 5f-h. Reagents and conditions: i: Pd(PPh 3 ) 4 (3 mol-%), K 3 PO 4 (6 equiv.), 1,4-dioxane, reflux, 6 h. Eur. J. Org. Chem. 2005, 4815-4828 www.eurjoc.org (3.213 g, 35 %) as yellowish oils (combined yield: 75 %). Spectroscopic data of E-2i: 1 H NMR (CDCl 3 , 300 MHz): δ = 1.26 (t, J = 7.2 Hz, 3 H, CH 3 ), 1.82-1.91 (m, 1 H, CH 2 ), 2.22-2.31 (m, 1 H, CH 2 ), 2.99-3.08 (m, 1 H, CH 2 ), 3.21-3.32 (m, 1 H, CH 2 ), 4.13 (q, J = 7.2 Hz, 2 H, OCH 2 ), 4.80 (q, J = 7.5 Hz, 1 H, OCH), 5.23 (dt, J = 10.5, 1.2 Hz, 1 H, CH 2 =CH), 5.31 (dt, J = 9.9, 1.2 Hz, 1 H, CH 2 =CH), 5.36 (t, J = 1.2 Hz, 1 H, CH=C), 5.80-5.91 (m, 1 H, CH=CH 2 ) ppm. 13 C NMR (CDCl 3 , 75 (s), 993 (s), 934 (m), 886 (s), 854 (w), 825 (s) cm -1 . MS (EI, 70 eV): m/z (%) = 182 (58) [M] + , 153 (4), 137 (100), 108 (27), 95 (24). C 10 H 14 O 3 (182.219): calcd. C 65.92, H 7.74; found C 65.30, H 7.88. The synthesis of Z-2i has been reported previously. [9]
Benzo[e]isobenzofuran. Formation and reactions of the parent and alkoxy-substituted derivatives
The Journal of Organic Chemistry, 1983
Benzo[e]isobenzofwan (1) is formed by base-induced 1,4-elimination of either acetal 9 or 11 and may be isolated in high yield as a crystalline solid. Cycloaddition reactions of preformed 1 have been carried out with various dienophiles. These reactions may also be accomplished by heating the acetals in the presence of dienophiles and acid catalyst, where 1 is generated as an intermediate. The cycloaddition reaction of 1 and maleic anhydride is found to be reversible at higher temperature (slow at 60 "C). Unsymmetrical dienophiles react with 1 to give equal amounts of regioisomers, and evidence points to lack of regioselectivity under both kinetically controlled and equilibrating conditions. The acetals 9 and 11 are shown to interconvert with acid catalyst at 140 O C , where 1 is an intermediate of greater stability than the acetals; the equilibrium K for 9 + 11 is approximately unity. Various acid-catalyzed cycloaddition reactions of ortho esters 8 and 10, yielding polysubstituted phenanthrene derivatives, are described. Wege has recently reported1 the synthesis of benzo[e]isobenzofuran (1, naphtho[ 1,BcIfuran) by pyrolysis2 of the corresponding (dihydro)naphthyne-furan derivative and found that it is qualitatively more stable than the parent isobenzofuran 2. Our work in this area began with a novel 1 2 3 1,Celimination procedure3 leading to 2 and its 1-alkoxy analogue: and we have recently extended this approach to the linearly annulated benzo[flisobenzofuran 3.5 As anticipated, 3 appears to be more reactive than 2; while 3 has only been intercepted as a reactive intermediate, 2 is moderately stable in neutral solution. It was of interest to apply this methodology3p4 to prospective precursors of 1 and its alkoxy derivatives, in order to examine reactivity and regioselectivity features of this dissymmetric isomer of 3. In this paper we report the formation of the precursor acetals and ortho esters, the preparation of 1 by base-induced elimination of acetals, and the acid-catalyzed equilibration, via 1, of these regioisomeric acetals. In ad
Heterocycles, 2018
A diastereospecific intramolecular cyclopropanation of (3R,8R,8aS)-8-bromo-3-phenylhexahydrooxazolo[3,2-a]pyridin-5-one 1 and (3R,8S,8aS)-8-bromo-3-phenylhexahydrooxazolo[3,2-a]pyridin-5-one 2 to generate the corresponding enantiopure 3-phenylhexahydro-5H-cyclopropa-[3,4]pyrrolo[2,1-b]oxazol-5-ones 3 and 4 in high yield is described. The synthesis of chiral cyclopropanes remains a considerable challenge, especially due to the fact that cyclopropane rings are often found in a variety of natural products and biologically active compounds. Organic chemists have always been fascinated by the cyclopropane subunit which has played and continues to play a prominent role in organic chemistry. Its strained structure, interesting bonding characteristics and value as an internal mechanistic probe have attracted the attention of the physical organic community. 1 Simmons-Smith cyclopropanation reaction is one of the most widely used reactions in the organic chemist's arsenal for the conversion of olefins into cyclopropanes. This popularity is mainly due to the stereospecificity of the reaction with respect to the double bond geometry and its compatibility with a wide range of functional groups. The chemoselectivity of the reaction toward some olefins is excellent and very few side reactions are observed with functionalized substrates. 2,3 Many of these reactions proceed in a cheletropic manner and several methods exist for converting alkenes to cyclopropane rings using carbene type reagents. As carbenes themselves are highly reactive it is common for them to be used in a stabilized form, referred to as carbenoid. The metal carbenoid is electrophilic in nature and electron-rich alkenes usually react much faster than electron-poor alkenes. In
The anti and syn @-eliminations from a series of 3 1 2,3-dihalo-2,3-dihydrobenzofurans (to give 3-halobenzofuran) have been kinetically investigated in t-BuOK-t-BuOH, in the presence and in the absence of 18-crown-6 ether (1 8C6), and in EtOK-EtOH. Reaction mechanisms have been assigned on the basis of leaving group, kinetic deuterium isotope, ring substituent (5-chlorine), and @-halogen effects. These data have provided information concerning structure and solvent effect on the mechanism generation, has been t h e most thoroughly studied alkoxy in the gas and liquid phases. Higher homologues have, however, received some attention and studies on a-cumyloxy have been of particular importance because of its involvement in cumene a~t o x i d a t i o n .~ Walling and co-workers6 were the first to study cumyloxy kinetics and obtained values of the rate constant ratio k,/k,, where ( 5 ) Howard, J. A,; Bennett, J. E.; Brunton, G. Can. J . Chem. 1981, 59, (6) (a) Walling, C.; Padwa, A.
Turkish Journal of Chemistry, 2006
The key compounds vinyl iodides 12a and 13a, for the generation of 1-cyclohept-1,2-dien-1-ylbezene (1), were synthesized from cycloheptanone (5). Bromobenzene was converted to the Grignard reagent, which was condensed with 5. Dehydration of alcohol 6 gave alkene 7. Hydroboration of 7 followed by oxidation with PCC afforded ketone 9, which was converted to hydrazone 10. Treatment of 10 with iodine resulted in the formation of 12a and 13a. The other precursors, 12b and 13b, were synthesized from the reaction of 9 with PCl5. Reactions of 12a, b and 13a, b with KOtBu in a sealed tube at 185 °C gave the [2+4] and [2+2] dimer products 20 and 21, respectively. In addition, reactions of 12a, b and 13a, b with KOtBu under the same conditions in the presence of diphenylbenzoisofuran (DBI) as a trapping reagent afforded the [2+4] cycloadducts 24 and 25 in good yields.
Chemistry of Heterocyclic Compounds, 1988
The regiochemistry of the reaction of 1,2-and 1-substituted derivatives of l-buten-3-yne and its 4-and 2,4-substituted derivatives of the isoprenoid type with acetoacetic ester and acetylacetone in the presence of the manganese(III) acetate-~opper(II) acetate oxidative system was studied. Derivatives of 4,5-dihydrofuran, furan, and hexahydrobenzofuran were obtained.
Russian Journal of Organic Chemistry, 2007
Zinc enolates obtained from 2,2-dibromoindan-1-one or 2,2-dibromo-1-tetralone and zinc reacted with alkyl esters and amides of 2-oxochromen-3-carboxylic acid giving the corresponding derivatives of 2,1'-dioxospiro(1a,7b-dihydrocyclopropa[c]chromen-1,2'-indan)-or 1',2',3',4'-tetrahydro-2,1'-dioxospiro(1a,7b-dihydrocyclopropa[c]chromen-1,2'-naphthalene)-1a-carboxylic acids prevailingly in the form of a single geometric isomer.