Several α-fluorovinylphosphonates (6) have been synthesised from the Peterson olefination reaction applied to both aldehydes and ketones in conjunction with α-lithiated-α-fluoro-αtrimethylsilylmethylphosphonate ( 2). The reaction with aldehydes gives mainly the E-isomer whereas reaction with ketones gives mainly the Z-isomer. We propose a closed transition state to explain the results of our study.

When (EtO) 2 P(O)CF 2 Br (1) is treated with isopropylmagnesium chloride in THF at low temperature it gives a magnesium species (2) which undergoes reactions with strong electrophiles (HCl, TMSCl, halogens, aldehydes and ketones). The formation of products strongly depends on the reaction conditions. With 1.5 equivalents of (2) between -78°C and 0°C, a conversion of more than 90% of aldehydes and ketones into 2-hydroxyphosphonates ( 7) and ( 8) can be achieved. These compounds ( 7) and ( 8) in the presence of base (NaH, LDA) are rearranged into 2,2-difluoroethylphosphates without concomitant formation of 1,1-difluoroolefines.

The reaction, under internal quench conditions, of diethyl dichloromethylphosphonate and symmetrical or unsymmetrical diaryl ketones in the presence of n-BuLi, leads to the corresponding symmetrical or unsymmetrical diarylalkynes via a Fritsch-Buttenberg-Wiechell rearrangement in a simple, high yielding, one-pot reaction.We recently reported an efficient synthesis of diethyl dichloromethylphosphonate (1) 1 which is known as a useful precursor for the preparation of dichloroalkenes from carbonyl compounds on a large scale. [2][3][4][5] As a component of another project we required preparative access to symmetrical or unsymmetrical diarylalkynes for [4+2] cycloaddition reactions. There are several methods reported in the literature 6 for the synthesis of these types of alkynes and we will just mention the more relevant one. Diarylalkynes are currently prepared via an oxidative coupling between aryl or substituted aryl halides and copper(I) acetylides in pyridine 7-9 or with terminal alkynes catalyzed by palladium at elevated temperatures. 10, 11 In the presence of copper(I) iodide, the palladium-catalysed reaction proceeds under mild conditions and gives the diarylalkynes in good yield. 12 This methodology has been widely used in the preparation of a variety of functionalised diarylalkynes. 11-16 Another approach uses the formation of diarylalkenes obtained by a Wittig-Horner reaction from arylmethylphosphonate esters and the corresponding aldehydes. After bromination of the alkenes and an elimination, effected with a base, the diarylalkynes are isolated. A recent preparation of dipyridylalkynes uses this process. 17 In the same way, [aryl(chloro)methyl]phosphonate has been introduced as an efficient reagent for the synthesis of phenylpyridylalkynes. 18,19 It is known that alkynes can equally be obtained through the Fritsch-Buttenberg-Wiechell rearrangement (1894) with 1,1-dibromoalkenes as starting materials. 20-22 Ihe reaction proceeds through the formation of an alkylidene carbene intermediate produced by an a-elimination of the 1,1-dibromoalkene (Scheme 1). However, as recently reported, the reaction is frequently non-specific, giving mixtures of compounds. [23][24][25] As previously described in our synthesis of chloroalkynes and terminal alkynes 1 we use internal quench conditions. Simultaneous addition of 1 and the prospective ketone 2 to LiHMDS in THF solution at low temperatures leads to a phosphorylated carbanion which is only present for a short period before it reacts with the ketone 2 to give the non-isolated gem-dichloroalkene 3. These conditions thus eliminate the possibility of decomposition of the phosphorylated carbanion to unwanted products. The reactions are easily monitored by 31 P NMR spectroscopy as on warming to room temperature the end of the first stage of the reaction is signalled by a single lithiophosphate peak [ 31 P NMR (THF): d = +0.4]. Next, the reaction medium is cooled to -60°C and two equivalents of n-BuLi are added followed by slow (40 min) warming to 0°C. This procedure gives ...