Bestmann reagent

This was prepared in four steps, starting with the formation of the vinyl cyclopropane, upon reaction with dimethyl-malonate and l,4-dibromobut-2-ene. Ozonolysis of the vinyl cyclopropane afforded the aldehyde, which was reacted with the Bestmann reagent to afford the alkyne substituted cyclopropane, 3. The cyclopropane was complexed with cobalt to afford the cobalt hexacarbonyl cyclopropane 4 in 85% yield. 

This intermediate was allowed to react with electrophiles such as DMF to obtain (/ p)-pseudo-6>r /i6>-diformyl[2.2]paracyclophane (/ p)-39 in 71 % isolated yield (Scheme 11). Enantiomer (Sp)-39 was obtained in 87 % isolated yield from (Sp,S)-2 through the same route. The formyl groups of (/ p)-39 were converted into the ethy-nyl groups using the Ohira-Bestmann reagent to give enantiopure (/ p)-pseudo-(9rr/i6>-diethynyl[2.2]paracyclophane (/ p)-40 in 60 % isolated yield the enantiomer (5p)-40 was similarly obtained in 57 % yield. 

Formation of Triazoles Using the Bestmann-Ohira Reagent. 174... 

In another series of experiments, the Ley research group [42] has used a Bestmann-Ohira reagent (dimethyl 1-diazo-2-oxopropylphosphonate [43]) to synthesize various alkynes and triazoles starting from aldehydes in the same Vapourtec system [38] combined with Omnifit glass columns [41]. 

Scheme 17 Flow synthesis of terminal alkynes using the Bestmann-Ohira reagent [42]...

Scheme 19 A three-step synthesis of triazole using Bestmann-Ohira reagent starting from an alcohol [42]...

Baxendale IR, Ley SV, Mansfield AC et al (2009) Multistep synthesis using modular flow reactors Bestmann-Ohira reagent for the formation of alkynes and triazoles. Angew Chem Int Edit 48(22) 4017 021... 

Purchased from Aldrich Chemical Company. The addition of this reagent is not necessary but is known to greatly expedite the reaction. A patent claim from H. J. Bestmann etal. is impending for this major improvement. 

As seen in the last example, the configuration of the double bond is conserved in the reaction. When Mn02 is used in combination with the Bestmann-Ohira reagent, activated alcohols are converted into terminal alkynes. ... 

Habermann, J., Ley, S. V. The Bestmann yiide as a multi-purpose wittig reagent. Chemtracts 200, 14, 386-390. 

Bestmann and Schulz describe a method for the synthesis of a,B-unsaturated y-keto esters illustrated by the reaction of phenacyl bromide with two moles of the Wittig reagent (2), triphenylphosphineearbomethoxymethylene. Presumably the... 

A similar approach had been reported earlier by Bestmann and coworkers" in their synthesis of hexadeuteriated leukotriene A4 methyl ester. C-alkylation of the tetrahy-dropyranyl ether of 3-butyn-l-ol with 2,2,3,3-tetradeuterio-l-iodopentane, prepared in 4 steps from propargyl alcohol, and subsequent protective group removal afforded the tetradeuteriated acetylenic alcohol 46 (equation 30). Semideuteriation of the alkynol and further transformation by known methods produced the labeled key reagent 3,4,6,6,7,7-hexadeuterio-(Z)-(3-nonen-l-yl)triphenylphosphonium iodide (47). Wittig olefination of epoxy dienal 45 with the labeled ylide generated from 47 completed the synthesis of... 

Gosney, 1. Rowley, A. G. In Organophosphorous Reagents in Organic Synthesis" Cadogan J. 1. G. Ed. Academic Press New York, 1979 Chap. 2. Bestmann, H. J. Pure Appl. Chem. 1980,52,771. 

Another attractive TOP sequence involves use of a combination of the Bestmann-Ohira reagent and Mn02. In these examples, a range of activated alcohols are oxidized to the corresponding aldehydes, which in turn are efficiently trapped by the subsequently added alkynylating reagent (eq 103). 

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