Phosphonates alkenyl

AUcynylstannanes can cross-couple with a variety of other functional groups employing the Stille protocol. Couphng to acyl chlorides is a well-known procedure that affords aUcynylketones in respectable yields. Other reports include alkynyltin cross-couplings with a-haloethers and a-halocarbonyls, enol phosphinates and phosphonates, alkenyl(phenyl)iodonium salts, alkynyl halides, and allyl hahdes (Table 9.18). Alkynylstannanes have also been shown to cross-couple with iron halides under the Stille conditions to effectively form iron-carbon bonds. 

The b ase-cadilyzed reacdon of ilialkyl phosphite with nitroalkenes results in the formadon of alkenyl phosphonates fEq. 4.33. ... 

Stereoselective alkenylation reactions have been achieved using chiral additives or auxiliaries. Ylids formed from phosphinoxides / jP—CHRR phosphonic... 

The base-catalyzed reaction of dialkyl phosphite with nitroalkenes results in the formation of alkenyl phosphonates (Eq. 4.33).39... 

Although not widely exploited, the use of the phosphonate 148 in Wadsworth-Emmons reactions represents a process of great potential that has been used to access the 3-alkenyl-l,2,4-oxadiazole 149 (Equation 21) <1989J(P1)2047>. 

The first example of asymmetric rhodium-catalyzed 1,4-addition of organoboron reagents to enones was described in 1998 by Hayashi and Miyaura. Significant progress has been made in the past few years. This asymmetric addition reaction can be carried out in aqueous solvent for a broad range of substrates, such as a,/ -unsaturated ketones, esters, amides, phosphonates, nitroalkenes. The enantioselectivity is always very high (in most cases over 90% ee). This asymmetric transformation provides the best method for the enantioselective introduction of aryl and alkenyl groups to the / -position of these electron-deficient olefins. 

In addition, aryl triflates have proven to be viable substrates for the Pd-catalyzed Csp2—P bond formation reactions [87-90], Intriguingly, phosphorylation can be achieved from the Pd-catalyzed coupling of alkenyl triflate with not only dialkylphosphites, but also with hypophosphorous acid [88]. Thus, phosphinic acid 87 was obtained when triflate 86 was treated with hypophosphorus acid in the presence of Pd(Ph3P)4. Due to the abundance of alkenyl triflates and milder reaction conditions, alkenyl triflates have certain advantages over the corresponding alkenyl halides as substrates for Pd-catalyzed phosphorylations to make alkenyl phosphonates or phosphinates. 

When methylene bisphosphonate (169) is reacted in a Horner reaction with an aromatic aldehyde, the alkenyl phosphonate 170 is produced (Scheme 5.25). By metalation with LDA in THF, this is converted to the vinyllithium intermediate 171 that, with the ketone 172, affords a Baylis-Hillman reaction-type product, 173 on base treatment, this is converted to the arylallene 174 [67]. 

The nucleophilic addition of NaN3 leads to 2-azido-2-alkenyl phosphonates 145, which would react further with PPh3 to afford phosphinimine 147. The migration of the C=C bond in 145 was not observed. Upon photolysis, 145 can also cydize to afford azirine 146 (Scheme 10.71) [76]. 

The migration of a C=C bond to form a C=N bond was also observed with hydro-xylamine [78, 79], hydrazine [80, 81] and primary amines [82]. The /f iminylphos-phine oxide formed in the reaction may serve as a Wittig reagent in the presence of a base to react with a ketone or an aldehyde leading to ,/fun saturated alkenyl-imines 153 (Scheme 10.74). The phosphorus group can be a phosphonium salt as well as a phosphonate. 

Since the migration of a C=C bond to form a C=N bond is impossible, the corresponding reaction with diethylamine afforded 2-amino-2-alkenyl phosphonates (Scheme 10.75) [83a]. 

The intermediate product 162, formed from the nudeophilic addition of 1,2-alle-nic phosphonate or 1,2-allenic phosphine oxide with allylic alcohol, would also undergo a Claisen rearrangement to form 2-oxo-5-alkenyl phosphonate or phosphine oxide 163 [85], The rearrangement is accelerated by the carbanionic nature of the intermediate 162. For the conjugate addition step, the reaction temperature is crucial since the reaction at 0 °C afforded mainly /i,y-unsaturated product whereas a,/8-unsaturated products were formed at 20 °C. 

The ring opening of activated azetidin-2-one 317 by a phosphonate-stabilized carbanion yielded the /3-ketophos-phonate 318 (Equation 109) <2002TL9641>. The Horner-Wadsworth-Emmons alkenylation and subsequent reduction of the latter compound affords a /3-aminoketone, which is used in the synthesis of sphingosine and phytosphingos i ne. 

Condensations between aldehydes and metalated phosphonic acid dialkyl esters other than those mentioned previously are also referred to as Homer-Wadsworth-Emmons reactions. Nevertheless, in these esters, too, the carbanionic center carries a substituent with a pi electron withdrawing group, for example, an alkenyl group, a polyene or a C=N group. The Homer-Wadsworth-Emmons reactions of these reagents are also stereoselective and form the new C=C double bond /ra/ ,v-selectively. 

Alkenyl-3-phosphoryl chromanones and their thio- derivatives (217) have been synthesized from lithiated allyl phosphonates (218) and salicylate. It is... 

Synthetically attractive arylation and alkenylation of a-bromoalkenyl phosphonates (471) with organo-boranes and -borates have been performed. Arylation was successful with the aryl boronic acids and a palladium catalyst, while alkenylation proceeded best with alkenyl borates, and a nickel catalyst (Figure 87). ... 

Sturtz et al. have described the deprotonation of the allyl bis(dimethylamido)phosphonate (9). Treatment of (9) with two equivalents of base, followed by reaction with an epoxide and hydrolysis, yields the y-lactone (Scheme 10). Alkylation with alkyl and alkenyl halides occurs at the y-carbon and hydrolysis yields the saturated and unsaturated carboxylic acids respectively. 

Alkenyl, Alkynyl, Aryl, Heteroaryl and Related Acids. - Alkenyl-phosphonates have been prepared by the dehydration of P-hydroxyphosphonates with DCC and CuCh, by dehydrohalogenation of P-bromoalkylphosphonates with triethyl orthoformate, and from alk-l-ynylphosphonates 116 by hydrogenation using Lindlar s catalyst (to give the m-isomer 118) and by stereoselective addition of alkylcuprates to give 117 (Scheme 7). A convenient... 

Under high-pressure (0.8 GPa) the alkenylation of carbonyl compounds 196 with phosphonate 197 [Horner-Wadsworth-Emmons (HWE) reaction] is accomplished efficiently (50-90% yields) at room temperature in the presence of triethylamine without further activation by Lewis acid. In contrast, reactions carried out at atmospheric pressure give negligible yields (0—8%) (Scheme 7.50). 

CM has also been applied in the immobilization of biologically active molecules. Thus, [230] Reetz and co-workers supported chiral phosphonate as a potential suicide enzyme inhibitor by reacting alkenyl phosphonates with either allyl-modified SIRAN (a porous glass) or allyl-modified TentaGel in the presence of the Grubbs catalyst in CH2CI2 at reflux. 

Ohler, E., Zbiral, E., and El-Badawi, M., A novel and versatile synthesis of heterocyclic aldehydes using dialkyl 3-oxo-l-alkenyl-phosphonates, Tetrahedron Lett., 24, 5599, 1983. 

Maruszewska-Wieezorkowska, E., and Michalski. J., Alkyl and alkenyl pyridines. Part 9. Phosphonates and tertiary phosphine oxide containing 2- and 4-pyridylmethyl groups at the phosphorus atom, and some of their reactions, Rocz. Chem.. 38. 625. 1964. 

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