Academic literature on the topic 'Vinyl-2 cyclobutanones'

A series of α-diazoketones, 8, 25, 28, 31, and 34, have been synthesized and their reaction with ethyl vinyl ether examined under various reaction conditions. In the presence of metal salts (Rh2(OAc)4, Pd(OAc)2, CuCl) the ethoxy-dihydrofurans 12, 37, 39, 41, and 43 are produced. Sensitized irradiation of the α-diazoketone 8 afforded the dihydrofuran 12 plus cyclobutanone 7, while direct photolysis of α-diazoketones 8, 25, 28, 31, and 34 gave the cyclobutanones 7, 38,40,42, and 44, respectively. A sample of the cyclopropylketone 45 was isolated from the rhodium(II) acetate mediated reaction of 34 and its facile rearrangement to dihydrofuran 43 demonstrated. Collectively, these results indicate that the initial product from the reaction of an α-diazoketone with an electron-rich alkene such as ethyl vinyl ether is a cyclopropylketone. The donnor–acceptor substitution pattern of this intermediate results in spontaneous rearrangement to a dihydrofuran. Thus a direct dipolar cycloaddition mechanism is not involved when α-diazoketones react with enol ethers under metal-mediated conditions. Instead, these reactions follow a cyclopropanation rearrangement or, more accurately, cyclopropanation – ring opening – cyciization pathway. Key words: diazoketone, rhodium acetate, dihydrofuran, cyclopropylketone, vinyl ether.

The fused 2-vinyl or 2-phenyl substituted cyclobutanones 4 undergo stereoselective ring openings by the action of alkoxide ions (t-BuO− or MeO−) to produce novel vicinally disubstituted cycloalkene derivatives 5 and 6 in moderate to high yields. The ring cleavage usually occurs with complete regioselectivity. The accessibility of γ,δ-unsaturated ester or acid derivatives makes this transformation a good supplementary method for the well-established Johnson–Claisen rearrangement.

Cette thèse décrit une voie d'accès aux cyclopropanols chiraux et en étudie les potentialités synthétiques. Préparé à partir du méthyl-2 succinate de n-butyle, l'hydroxy-1 méthyl-2 cyclopropanecarboxaldéhyde est un précurseur de (vinylcarbinol)-1 cyclopropanols lesquels, subissent en milieu acide soit une extension de cycle C3→C4 régiospécifique en vinyl-2 cyclobutanones (BF3-Et20), soit une extension de cycle C3→C4→C5 en cyclopentène-2 ones (CH3S03H-P205). La réaction thermique des méthyl-2 vinylcyclopropanes donne par ène-réaction des produits d'ouverture de cycle limitant l'intérêt du réarrangement vinylcyclopropane-cyclopentène ; ce problème est contourné par cette nouvelle approche. Les (R)(+) et (S)(-) méthyl-2 succinates de méthyle, préparés par résolution enzymatique à l'aide de la lipase du pancréas de porc, sont cyclisés par réaction du type acyloïne en (R) et (S) méthyl-3 disiloxycyclobutènes respectivement. Ceux-ci par régression de cycle stéréosélective C4 → C3 en milieu basique, donnent accès sans altération du centre chiral à des hydroxy-1 cyclopropanecarbo­ xaldéhydes, utilisés pour préparer des (vinylcarbinol)-1 cyclopropanols optiquement actifs. Une extension de cycle C3→C4 régio- et stéréospécifique conduit alors aux vinyl-2 cyclobutanones avec une très bonne énantiosélectivité. Ces composés ont été utilisés pour préparer la (S)(+) méthyl-5 cyclohexène-2-one et un buténolide : la quercus lactone b. Les vinyl-2 cyclobutanones sont des précurseurs de cycle en C5, C6 et C8, cette méthodologie, ne mettant pas en jeu d'ions cyclopropylcarbinyl vrais comme le prouve la stéréospécificité des réarrangements, permet donc, à partir de succinates chiraux, d'envisager la synthèse totale de produits naturels de structures variées
The aim of this thesis is the preparation and study of the synthetic potential of chiral cyclopropanols. The 1-hydroxy 2-methyl cyclopropanecarboxaldehyde available from 2-methylsuccinate, is used to prepare 1-(vinylcarbinol} cyclopropanols which, undergo acid induced C3 C4 regiospecific ring expansion into 2-vinyl cyclobutanones (BF3-Et20) or C3 -+ C4 --+- C5 ring expansion into cyclopenten-2- ones (CH3S03H-P205). The thermal rearrangement of 2-methyl vinylcyclopropanes leads by an ene-reaction to ring-opened products ; therefore the limitation of the thermal vinylcyclopropane-cyclopentene ring enlargement is removed by this new approach. (R)(+) and (S)(-). Dimethyl 2-methylsuccinates, now available from enantiose­ lective hydrolysis by porcine pancreatic lipase, undergo acyloin type cyclization into (R) and (S) 3-methyl-1,2-disiloxycyclobutene, respectively. Base-induced stereoselective C4 C3 ring contraction of these cyclobutenes provides 1-hydroxycyclopropanecarboxaldehydes which are used to prepare optically active 1-alkenylcyclopropanols. Then, acid-induced regio- and stereospecific C3---+ C4 ring enlargement leads to 2-vinylcyclobutanones with high enantiomeric excesses. These compounds are used to synthetize (S) 5-methyl cyclohexen-2-one and abutenolide ; i. E. The quercus lactone b2-Vinylcyclobutanones are efficient precursors of 5-, 6- and 8-membered rings. Therefore, this new methodology, which does not involve cyclopropylcarbiny1 cations as proven by the stereospecificity of the rearrangements, allows one to prepare from chiral succinates natural compounds bearing different frameworks

Building on the Tanino synthesis of glycinoeclepin (Organic Highlights, January 3, 2011), the hatch-stimulating substance for the soybean cyst nematode, Keiji Tanino of Hokkaido University and Masaaki Miyashita, now at Kogakuin University, described (Nat. Chem. 2011, 3, 484) a convergent synthesis of solanoeclepin A 3, the hatch-stimulating substance for the potato cyst nematode. A key step in the synthesis was the diastereoselective Diels-Alder cyclization of 1 to 2. The starting point for the synthesis was the conjugate addition of 5 to 3-methyl cyclohexenone 4, followed by aldol condensation. The secondary acetate corresponding to 6 was readily resolved by lipase hydrolysis. The next challenge was the installation of the angular vinyl group. Enone transposition gave 7, to which vinyl Grignard added with high diastereocontrol, leading to the diol 8. TMSOTf-mediated epoxide rearrangement with concomitant 1,2 vinyl shift then delivered 9. Epoxidation followed by Stork cyclization completed the construction of the cyclobutane 10. The allylic alcohol 12 was enantiomerically pure, so the relative configuration of the sidechain cyclopropane could be set by the Charette protocol. Grieco dehydration of 14 then gave 16, a latent form of the cyclobutanone of 3. Condensation of the ketone 17 with 18 delivered the expected keto enamine, which rearranged nicely on exposure to Tf2O to the aldehyde 19. Diastereoselective addition of the furyl lithium 20 followed by Pd-catalyzed coupling with 21 then completed the assembly of the Diels-Alder substrate 1. The Me2AlCl-mediated intramolecular Diels-Alder cyclization of 1 led to 2 with remarkable diastereocontrol. Oxidation gave 22, that was further oxidized to the protected enol 23. Reduction, alkene cleavage, and protecting group manipulation then set the stage for the final oxidation of 24 to solanoeclepin A 3.