Alkynyl phosphonates

The pyrazole analog 140 has been prepared from the reaction of the alkynyl phosphonate with ethyl diazoacetate, whereas the pyrazoline 139 was obtained under similar conditions with diediyl vinylphosphonate (78). 

Mashlyakovskii, L.N., and lonin, B.I., Unsaturated phosphonic acids and their derivatives. Part 1. Synthesis of alkadienyl-, aUtenynyl-, and alkynyl-phosphonic dichlorides, Zh. Obshch. Khim., 35, 1577, 1965 J. Gen. Chem. USSR (Engl. Transl.). 35, 1582, 1965. 

Phosphoroisocyanatidites (e.g. 83) react with 3-alkylidene-2,4-pentanediones (e.g. 84a) or 2-alkylideneacetoacetic esters (e.g. 84b) to form phosphoranes (85,a,b) which decompose on heating to the cyclic phosphonates (86a, b)27. in an analogous study, dialkylalkynylphosphonates (87) have been shown to react with alkyl pyruvates (88) below 0°C to form mixtures of alkynyl phosphonates (90) and monocyclic tetraoxaphosphoranes (91) via (89)28. At 80°C, however, (89) reacts with excess (88) via (92) to form the bicyclic phosphorane (93). 

One route to (l-alkynyl)phosphonic esters depends on the base-catalysed destruction of enol phosphates (123) obtained in situ from (2-oxoalkyl)phos-phonates in the case of (123) (R = Et), a mixture of (1-butynyl)- and (2-butynyl)-phosphonic esters was obtained, but in all other quoted cases only the acetylenic compound was obtained. A second route starts with diethyl (trichloromethyl)-phosphonate (a reagent of increasing synthetic importance) followed by sequential reaction in one-pot with BuLi (two equivalents), an aldehyde (RCHO), and a lithiumdialkylamide, and gives the products (Et0)2P(0)CsCR in very high yields. ... 

IV. THE FORMATION OF P—C(sp) BONDS. SYNTHESES OF ALKYNYL PHOSPHONIC AND PHOSPHINIC ACIDS... 

The formation of alkynephosphonic diesters through the isomerization of alkynyl phos-phorus(III) esters and subsequent prototropic rearrangement of the propadienylphos-phonic acid derivatives has already been discussed. An early listing of alkynyl-phosphonic and -phosphinic acid derivatives (and also related types of organophosphorus compounds) is available ... 

G. Miscellaneous Synthetic Reactions for Alkenyl and Alkynyl Phosphonic Acids... 

Esters and other derivatives of alkenyl- and alkynyl-phosphonic acids, and of the correspondingly unsaturated phosphinic acids, undergo a wide range of addition and cycloaddition reactions which will be considered more fully in Chapter 6. These reactions include applications of the Diels-Alder reaction to yield carbocyclic phosphonic acids based on mono- and poly-cyclic ring systems, some of which are precursors to other aromatic phosphonic acids. A typical example of this procedure is the addition of dimethyl (bromoethynyl)phosphonate to 2,3-dimethylbutadiene elimination of HBr from the 1 1 cycloadduct, using Et3N, affords dimethyl (2,3-dimethylphenyl)phosphonate. The addition of carbenes to alkenylphosphonic derivatives yields those of cyclopropylphos-phonic acids. ... 

Other addition reactions include those of dialkyl hydrogenphosphonates to alkynyl-phosphonic esters under basic catalysis, observed by Saunders and Simpson" and by others (reaction 51) but also of some interest are those additions of hydrogenphosphonates to acetylenic alcohols such as 376 (Scheme 15). The addition of hypophosphorous acid to the alcohols 380 affords the alka-l,2-dienephosphinic acids 381 which, when treated with acid, cyclize to the acids 382 . ... 

Ruthenium-catalyzed [2 + 2] cycloadditions involving bicyclic alkadienes (377) and alkynyl phosphonates (378) have been investigated by Tam and co-workers. The corresponding cyclobutene cycloadducts (379) were obtained in low to excellent yield (up to 96%) (Scheme 87). Alkynyl phosphonates showed a lower reactivity than other heteroatom-substituted alkynes such as alkynyl halides, ynamides, alkynyl sulfides, and alkynyl sulfones and required a higher reaction temperature and much longer reaction times. 

Scheme 4.23 Ketenes from alkynyl phosphonates in insecticidal action.

Dialkyl (l-hydroxy-2-alkynyl)phosphonates [e.g. (64)], prepared by addition of lithium acetylides to acyl phosphonates, can be converted regioselectively into allenic phosphates via the phosphonate-phosphate rearrangement (e.g. Scheme 104). If sodium alkoxides in alcohols are used to effect the rearrangement, mixtures of allenic and acetylenic products are formed however, use of sodium bis(trimethylsilyl)amide in DMSO furnishes allenic phosphates almost exclusively. 

Different heteroatom-substituted alkynes have been involved in this reaction such as alkynyl halides [78, 79] [Eq. (32)], ynamides [76, 77], alkynyl sulfides or sulfones [80], and alkynyl phosphonates [81], Haloalkynes were found to be the most reactive, proceeding at room temperature, whereas alkynyl phosphonates showed the lowest reactivity. 

The ruthenium-catalysed homo Diels-Alder [2+2+2] cycloaddition reaction between alkynyl phosphonates (601) and bicyclo[2.2.1]hepta-2,5-diene (600) providing the corresponding phosphonate substituted delta-cyclenes (602) in low to good yields (up to 88%) as studied by Kettles, Cockburn and Tam (Scheme 148). ... 

Srebnik has reported the synthesis of phosphono boronates by hydroboration with pinacol borane (30) [92]. The reaction proceeds well with terminal alkenyl phosphonates whereas internal alkenyl phosphonates gave complex mixtures. Hydroboration of the corresponding alkynyl phosphonates under identical conditions gave alkenyl phosphonates that were difficult to isolate and were in situ subjected to Suzuki coupling with phenyl iodide to give trisubstituted phosphonates providing a new one-pot synthesis of this class of compounds (Scheme 3.60). 

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