Allylic Hydroxy Phosphonates Research Articles

ChemInform Abstract: Synthesis of Cyclopentenones via Intramolecular HWE and the Palladium‐Catalyzed Reactions of Allylic Hydroxy Phosphonate Derivatives.

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Synthesis of Cyclopentenones via Intramolecular HWE and the Palladium-Catalyzed Reactions of Allylic Hydroxy Phosphonate Derivatives

Palladium-catalyzed decarboxylative rearrangement of nonracemic phosphono allylic acetoacetates, or the intermolecular allylic substitution of nonracemic phosphono allylic carbonates with tert-butyl acetoacetate followed by hydrolysis and decarboxylation, gave omega-ketovinyl phosphonates. A highly regioselective Wacker oxidation gave the omega,beta-diketophosphonates which underwent intramolecular HWE reaction to give nonracemic cyclopentenones. An aldol condensation leading to phosphonocyclopentenones was competitive with the HWE reaction. The stereochemistry of the cyclopentenone and the ratio of HWE to aldol products were dependent upon the choice of base used in the reaction.

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).

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.

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

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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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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.

Palladium Catalyzed Additions to Allylic Hydroxy Phosphonates: Applications in the Enantioselective Synthesis of Enterolactone and Turmerone

Reaction of nonracemic allylic hydroxy phosphonates, prepared by the asymmetric phosphonylation of unsaturated aldehydes, with methyl chloroformate in pyridine yields the corresponding carbonates. The carbonates are excellent substrates for the palladium-catalyzed addition of nucleophiles. Addition of the nucleophile is highly regioselective, resulting in n -substituted vinyl phosphonates. The reaction of the allylic carbonates with aryl stannanes and malonates has been investigated. Progress in the application of these reactions to the synthesis of turmerone and enterolactone is reported.

Formation of Cyclic Acetals from Allylic Hydroxy Phosphonates via Intramolecular Oxymercuration

Treatment of allylic hydroxy phosphonates in aldehyde solution with mercuric trifluoroacetate, followed by the reduction of the organomercurial intermediate, afforded the cyclic acetal derivatives. The reaction displays high diastereo- and regio-selectivity. 31 P NMR studies showed the formation of an intermediate hemiacetal and rapid formation of the organomercurial upon addition of mercuric trifluoroacetate. However, the oxymercuration was reversible, and attempts to remove the excess aldehyde often led to recovery of the starting material. Fortunately, reduction of the organomercurial intermediate with sodium cyanoborohydride in the presence of the aldehyde led to more reproducible yields.

Stereoselective Reactions of Allylic Hydroxy Phosphonates

The stereochemical outcome of the palladium catalyzed addition of nucleophiles to the carbonate derivative, the [3,3] rearrangement of the imidate and carbamate derivatives, and the epoxidation and cyclopropanation of hydroxy allylic phosphonates is presented.

Stereoselective Reactions of Allylic Hydroxy Phosphonates

The stereochemical outcome of the palladium catalyzed addition of nucleophiles to the carbonate derivative, the [3,3] rearrangement of the imidate and carbamate derivatives, and the epoxidation and cyclopropanation of hydroxy allylic phosphonates is presented.