Allyl phosphonates addition reactions

The reaction of perfluoroalkyl iodides with alkenes affords the perfluoro-alkylated alkyl iodides 931. Q.a-Difluoro-functionalized phosphonates are prepared by the addition of the iododifluoromethylphosphonate (932) at room temperature[778], A one-electron transfer-initiated radical mechanism has been proposed for the addition reaction. Addition to alkynes affords 1-perfluoro-alkyl-2-iodoalkenes (933)[779-781]. The fluorine-containing oxirane 934 is obtained by the reaction of allyl aicohol[782]. Under a CO atmosphere, the carbocarbonylation of the alkenol 935 and the alkynol 937 takes place with perfluoroalkyl iodides to give the fluorine-containing lactones 936 and 938[783]. 

A-trityl-(l/ ,2S)-norephedrine (58), the corresponding allyl phosphonates 62a,b were obtained via the Arbusov rearrangement of 2-ethoxy-1,3,2-oxazaphospholidine 60. The absolute configuration of the major diastereomer, 62a was determined by X-ray as (2S1,45,51 ).The reaction of the major diastereomer of allyl phosphonates 61a and 62a with DBU afforded the corresponding vinylphosphonates 63a,b (Scheme 21) [48], Nucleophilic addition to these resulted in induction of chirality at the [1-position of the stereogenic phosphorus atom in the initially produced diastereomeric phosphonates 64 or 65 (Scheme 21) [48],... 

The formation of keto-phosphonate structure within macromolecule leads to the removal of internal unsaturation. Triallyl cyanurate and ionizing irradiations [210] made a E-P block copolymer-PE blend thermally stable. Triallyl cyanurate increases the crosslinking density probably due to addition reactions between polymeric and allyl radicals produced by ionizing radiation. The addition of 2,2,4-trimethyl-l,2-di-hydroquinoline and bis[4(l-methyl-1-phenylethyl)pheny 1]-amine stabilized a PE-EPDM blend against heat [211]. Popov et al. [212] studied the ozone effect on PE-iPP blend. The oxidation rate was detected in relation to... 

The 1,4-addition reaction of stabilized allylic carbanions with conjugated enones is normally complicated by the ambident reactivity of the carbanion. Clean 7-selective conjugate addition to cyclic enones, however, has been observed with lithiated allylic sulfoxides, phosphine oxides and phosphonates... 

Conjugated dienes undergo hydroperfluoroalkylation with perfluoroalkyl iodides and zinc in the presence of titanium catalysts 02 Yields are moderate to good (52-74%) but stereoselectivity is low. From allylic halides functionalized on the a-vinylic position (TMS, carboxylate, phosphonate), additions to terminal alkynes provide functional dienes, used in further synthetic reactions leading to lactones and carboxylic or phosphonic esters.228... 

Other allylic compounds which participate in addition fragmentation reactions and yield telecheUcs analogous to allylic sulfides include allylic bromides, allylic phosphonate, allyl peroxides, and allylic stannane and vinyl ethers (62). 

While the use of this reaction for the preparation of alkenes is well documented, and discussed (vide infra), there are examples that extend the use of this chemistry. Dauben" reported the synthesis of cyelohexadienes using allyl phosphonates. Thus exposure of ketone 119 to ylide 120 afforded intermediate 121 by an initial Michael addition. Regeneration of the ylide to form 122, catalyzed by the resultant enolate, could then facilitate the ring closure to form the desired product 123. 

Tetrasubstituted allene 2,4-diethyl-2,3-pentadiene was also reacted with H-phosphonate, but the addition reaction was accompanied with double bond isomerization leading to a mixture of allyl- and vinylphosphonates. 

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. 

Conversion of allylic acetates of allylstannanes by treatment with Et2AlSnBus and Pd° catalysts proceeds by addition of the tin to the metal, followed by reductive elimination (equation 204).309 The corresponding ally phosphonate, however, showed some loss of stereochemical integrity (equation 205).310 The Pd°-catalyzed reaction of allylic acetates, trialkyltin chlorides and Smh produced allylstannanes with no stereospecificity.311... 

A general methodology for the construction of quaternary carbon atoms at the carbonyl carbon of ketones has been successfully exploited for the facile synthesis of ( )-lycoramine (299) (Scheme 30) (165). Thus, the O-allylated o-vanillin 322 was allowed to react with vinyl magnesium bromide followed by Jones oxidation, and the acid-catalyzed addition of benzyl IV-methylcarbamate to the intermediate a,(3-unsaturated ketone furnished 323. Wadsworth-Emmons olefination of 323 with the anion derived from diethyl[(benzylideneami-no)methyl]phosphonate (BAMP) provided the 2-azadiene 324. The subsequent regioselective addition of n-butyllithium to 324 delivered a metalloenamine that suffered alkylation with 2-(2-bromoethyl)-2-methyl-l,3-dioxolane to give, after acid-catalyzed hydrolysis of the imine and ketal moieties, the 8-keto aldehyde 325. Base-catalyzed cycloaldolization and dehydration of 325 then provided the 4,4-disubstituted cyclohexenone 326. The entire sequence of reactions involved in the conversion of 323 to 326 proceeded in very good overall yield and in one pot. 

Reactions with —OH Groups and Epoxides.—The formation of A -l,2-oxaphos-pholen derivatives from propargylic alcohols and phosphorus trichloride has been studied in detail. Intermediate phosphites (24) and allenic phosphonates (25) are described, and the A -l,2-oxaphosphoIen is produced in the final stage, as shown. Improved conditions have been outlined for the preparation of allylic bromides (26) from allylic alcohols and phosphorus tribromide. Related reactions of primary alcohols with the complex of phosphorus trichloride and DMF lead to the chloride (27) 22 addition of zinc bromide to the reaction results in the formation of alkyl bromides, but an attempt to extend this exchange to the preparation of cyanides was not successful. ... 

Most of the examples in this chapter have been disubstituted alkenes, a few have been trisubstituted, but none so far has been tetrasubstituted (except cyclic alkenes) as this is the most difficult case of all. One solution49 starts with ethyl lactate 228 and uses a HWE reaction on the enantiomerically pure phosphonate 229 to make the / -enone 230 with very high selectivity. Chelation-controlled addition of a Grignard reagent gives the stereochemically pure allylic alcohol 231. Chelation control is explained in chapter 21. 

The synthesis of Cbz-protected D-valine methyl ester (296) (Scheme 40) begins with addition of an organometallic reagent to the ester function of 282. The resulting phosphonate 290 undergoes a Wittig reaction with isobutyraldehyde to afford 291. Chelation-controlled reduction of the ketone with zinc borohydride furnishes the a /-alcohol 292 (98% de). A [3,3] rearrangement of trifluoroacetimidate 293 produces allylic amine 294. Elaboration of the olefin to an ester furnishes the D-valine derivative 296 with 85% ee [101]. 

Similar reactions can lead to the formation of two P-C bonds. For example, Pd-catalyzed addition of 7 (a privileged substrate which is often more reactive than other H-phosphonates) to terminal alkynes led to dehydrogenative double cis phosphonylation (Scheme 9). A Pd(II)/Pd(IV) cycle was proposed. Reaction of [Pd(allyl)Cl]2 with 7 gave chloro-bridged dimer 8. Alkyne insertion into the Pd-P bond was then proposed to give alkenyl intermediate 9. P-H oxidative addition would then yield hydride 10, whose reaction with 7 was proposed to lead to P-C bond formation and loss of H2 [18]. 

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