Allylic Phosphonates Research Articles

Synthesis and utility of new amine/nucleobase addition products of allenylphosphonates

In the reaction of allenylphosphonates with amines/nucleobases, depending on the amine and the allenylphosphonate, either Z- or E-vinylphosphonate or allylphosphonate as a single isomer with a β-amino functionality was isolated. A simple route to phosphonates with a β-NH 2 group is developed by direct reaction with ammonia. In reactions with adenine, three different modes of reaction, with one of them involving an unusual cyclisation, are observed. The utility of (enamino)allyl phosphonate products thus obtained in the synthesis of (enamino)-1,3-butadienes via Horner–Wadsworth–Emmons (HWE) reaction is also demonstrated.

3,3]‐Rearrangements of Phosphonium Ylides.

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Synthetic Studies on Taxol: Highly Stereoselective Construction of the Taxol C-Ring via SN2‘ Reduction of an Allylic Phosphonium Salt

[reaction: see text] The highly stereoselective construction of the C3 stereogenic center of the taxol C-ring is described. The trans isomer at the C3-C8 position of the taxol C-ring, which is required for the total synthesis, as well as its diastereomeric cis isomer were successfully synthesized with highly diastereoselective S(N)2' reduction of the allylic phosphonium salts.

3,3]-Rearrangements of Phosphonium Ylides

Allylic phosphonium ylides are readily generated by the combination of an allylic alcohol, a carbene, and a chlorophosphite. Here we demonstrate that these intermediates undergo a thermal [3,3]-rearrangement to provide single isomers of homoallylic phosphonates in good to excellent yields. This new reaction manifold for phosphorus ylides is tolerant of a range of substitution patterns on the reactants and provides access to structurally complex intermediates for the synthesis of enzyme inhibitors, aminophosphonic acids, and natural products.

Electrochemical Partial Fluorination of Organic Compounds. 80. Synthesis of Cyclic α-Arylthio-α-monofluorophosphonate Esters

[Reaction: see text]. Seven-membered cyclic alpha-monofluorophosphonate esters such as 2-allyloxy-3-fluoro-3-phenylthio-4,7-dihydro-[1, 2]-oxaphosphinine-2-oxide were successfully synthesized in moderate total yield as 41% from open-chain allyl phosphonates having an alpha-arylthio group as an electroauxiliary using an alternative sequence of anodic fluorination and ring-closing olefin metathesis (RCM). On the other hand, in an attempt to synthesize an eight-membered analogue, a different type of seven-membered fluorinated cyclic product was formed predominantly by the RCM reaction between the allyloxy groups.

A Convenient Synthesis of γ‐Methyl α‐(Alkylidene)‐γ‐butyrolactones.

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Allylic Hydroxy Phosphonates: Versatile Chiral Building Blocks.

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Synthesis of Nonracemic Allylic Hydroxy Phosphonates via Alkene Cross Metathesis.

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Allylic hydroxy phosphonates: versatile chiral building blocks

Allylic hydroxy phosphonates are converted into β and γ substituted amino phosphonates using a series of palladium-catalyzed reactions. The judicious selection of nitrogen nucleophile and palladium catalyst allow for excellent regio- and stereochemical control. Palladium(0)-catalyzed amine addition or tosyl carbamate rearrangement gives rise to the γ-substituted phosphonates, whereas, reaction of tosyl carbamates with palladium (II) and base gives oxazolidinones (β-substitution).

Regio- and stereoselective reactions between cyclic Baylis–Hillman type adducts and N-nucleophiles and P-nucleophile

New important organic compounds multifunctionalized cyclic 6-membered and 7-membered allylic amines, azide and phosphonates have been obtained via regio- and diastereoselective reactions of cyclic Baylis–Hillman type adducts 1 with N-nucleophiles and P-nucleophile. We have found that the reactions proceed by S N2 or S N2′ processes exclusively, or by both processes simultaneously. The S N2′ process occurs with anti stereochemistry.

Synthesis of Nonracemic Allylic Hydroxy Phosphonates via Alkene Cross Metathesis

Allylic hydroxy phosphonates and their derivatives can be interconverted by using cross metathesis with second generation Grubbs catalyst. The absolute stereochemistry of the starting phosphonate is conserved in the product. Cross metathesis reaction of the acrolein-derived phosphonate 2a yields a series of functionalized allylic hydroxy phosphonates. However, the cross metathesis reaction is often accompanied by competing dimerization and alkene migration reactions leading to a reduction in yield. The cinnamaldehyde- and crotonaldehyde-derived phosphonates 2b and 2c were also examined. In general, the metathesis reactions of phosphonates 2b and 2c are considerably slower than those for phosphonate 2a leading to mixtures. Several hydroxyl-protected derivatives of the phosphonate 2a (methyl carbonate 3a, acetate 4a, N-tosyl carbamate 5a, TBDMS 6a, and acetoacetate 7a) undergo metathesis without competing side reactions to give substituted allylic phosphonates in good to excellent yield.

Palladium Pincer Complex Catalyzed Allylic Stannylation with Hexaalkylditin Reagents.

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A Convenient Method for the Synthesis of Terminal (E)-1,3-Dienes

Lithiated allylic phosphonates undergo efficient olefination reactions with a variety of aldehydes in the presence of HMPA to give terminal 1,3-dienes with high selectivity for the E-isomer. This method is general and procedurally simple.

Stereospecific Pd(O)‐Catalyzed Malonate Additions to Allylic Hydroxy Phosphonate Derivatives: A Formal Synthesis of (‐)‐Enterolactone.

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Palladium pincer complex-catalyzed allylic stannylation with hexaalkylditin reagents.

Palladium pincer complex (1)-catalyzed stannylation of allyl chloride, phosphonate, and epoxide substrates (4a-h) could be performed with hexaalkylditin reagents (3) under mild neutral reaction conditions. This catalytic reaction proceeds via palladium(II) intermediates without involvement of allyl-palladium complexes, and therefore the allylstannane product does not interfere with the palladium catalyst. Use of a combined catalytic system (1 + 2) allowed the development of an effective one-pot procedure for allylation of aldehyde and imine electrophiles. [reaction: see text]

Stereospecific Pd(O)-catalyzed malonate additions to allylic hydroxy phosphonate derivatives: a formal synthesis of (-)-enterolactone.

A combination of cross-metathesis and malonate addition was applied to a formal synthesis of the mammalian lignan enterolactone 5. The cross-metathesis of alkene 6 and phosphonate 3a gave the substituted allylic phosphonate 3d. The palladium-catalyzed addition of malonate 10d to the allylic phosphonate 3d was stereospecific and highly regioselective and yielded the vinyl phosphonate 11d. The vinyl phosphonate 11d was converted in two steps into the lactone 14, a known intermediate in the synthesis of enterolactone 5.

Stereospecific Pd(0)‐Catalyzed Arylation of an Allylic Hydroxy Phosphonate Derivative: Formal Synthesis of (S)‐(+)‐ar‐Turmerone.

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Palladium-catalyzed asymmetric allylic substitution of 2-arylcyclohexenol derivatives: asymmetric total syntheses of (+)-crinamine, (-)-haemanthidine, and (+)-pretazettine.

Much interest has been shown in Amaryllidaceae alkaloids as synthetic targets due to their wide range of biological activities. Over 100 alkaloids have been isolated from members of the Amaryllidaceae family; most of them can be classified into eight skeletally homogeneous groups. We have succeeded in the first asymmetric total syntheses of the crinane-type alkaloids (+)-crinamine (1), (-)-haemanthidine (2), and (+)-pretazettine (3). The starting cyclohexenylamine 14 was obtained from allyl phosphonate 11c by palladium-catalyzed asymmetric amination in 82% yield and with 74% ee. The product was recrystallized from MeOH. Interestingly, (-)-14 with 99% ee was obtained from the mother liquor (74% recovery). Intramolecular carbonyl-ene reaction of (-)-10 proceeds in a highly stereoselective manner to give hexahydroindole derivative 9 as the sole product. In the Lewis-acid-catalyzed carbonyl-ene reaction, an interesting rearrangement product, 20, was isolated in high yield. From 9, (+)-crinamine was synthesized. Thus, the asymmetric total synthesis of (+)-crinamine was achieved in 10 steps from 11c, and the overall yield is 19%. The total synthesis of (-)-haemanthidine was also achieved from 9 by a short sequence of steps.

Stereospecific Pd(0)-Catalyzed Arylation of an Allylic Hydroxy Phosphonate Derivative: Formal Synthesis of (S)-(+)-ar-Turmerone

Reaction of the (1S)-allylic hydroxy phosphonate 1(S) with methyl chloroformate in pyridine yields the corresponding carbonate 3(S). The carbonate 3(S) undergoes a palladium-catalyzed arylation with p-tolyl tributylstannane to give both the 1E and 1Z vinyl phosphonates 6 (85:15). The E and Z vinyl phosphonates 6 were shown to have the opposite configuration at C-3. The major vinyl phosphonate isomer (3S,1E), was converted to (3S)-3-(p-tolyl)-butanal 8(S), completing a formal total synthesis of (S)-ar-turmerone 5a.

Fireproofing of polyurethane elastomers by reactive organophosphonates

AbstractPolyurethane elastomers were prepared with hydroxytelechelic polybutadiene (HTPB) as polyol, modified 4,4′‐diphenylmethane diisocyanate (modified MDI) as liquid polyisocyanate, and phosphonate diols as chain extenders and flame retardant compounds. These phosphonate diols were synthesized by radical thiol–ene addition of allyl or vinyl dialkyl phosphonate to 3‐mercapto‐1,2‐propanediol. For various percentages of phosphorus (0 to 3%, w/w), polyurethane elastomers remain stable up to 250 °C. The percentage of residual char at 600 °C increases with increasing phosphorus content. For the soft segments, no variation in the glass transition temperature (Tg) is observed as the percentage of P increases, whereas the Tg of hard segments increases. Above 0.5% phosphorus content, the limiting oxygen index (LOI) becomes higher than the percentage of oxygen in the air.© 2003 Society of Chemical Industry