Alkenylphosphonic derivatives, reactions with

The additions of thiols and sulphenyl chlorides to alkenylphosphonic derivatives to yield (2-alkylthioethyl)phosphonic compounds are reactions which have already been noted" Dialkyl (alkylthiomethyl)phosphonates yield a-chloro derivatives when treated with ncs in CCl/° the resultant dialkyl (l-alkylthio-l-chloromethyl)phosphonates undergo Friedel-Crafts arylation with benzene, alkylbenzenes or other activated aromatics in the presence of SnCl4 or TiCl/ yields are said to be good. 

The first successful preparation of phosphorus-containing heterocyclic fatty acid derivatives has been presented. Reaction of cx-keto allene (379) with trimethyl phosphite gave oxaphosphole derivative (380). Similar transformations with a-keto and a-chloro-ot-ketoallenes (381) and (382) led to the formation of alkenylphosphonates (383) and (384), respectively (Figure 64) ... 

The use of esters of a (substituted-methyl)phosphonic acid to provide the carbanion site next to phosphoryl phosphorus was a natural step forward. The most successful development has been the use of the carbanion 346 derived from esters of methylenebisphospho-nic acid (or its monoalkylated derivatives). The anion 346 reacts with an aldehyde to afford the alkenylphosphonic diester 347 (R = Et, Ph, PhCH—CH, 2-thienyl, 2-pyridinyl, etc,) ". Use of the protected 3-pyridinylcarboxaldehyde 348 allowed the preparation of the ester 349, which, after reduction of the C=C bond and hydrolysis, afforded the phosphonic acid 350 Such reactions have also been carried out under phase-transfer condi-tions. Reactions between the lithium salt of the ester 351 and benzaldehyde or but-2-enal give the (alk-1 -enyl)phosphonic esters 352 and 353 in the ratio 1 4 the lithium salts 354 and 355 are formed concomitantly in the ratio 4 1. ... 

On the other hand, high Z-selectivity is seen in the olefination reactions of the carbanion 19 derived from 3,3-diethoxybutylphosphonate with aldehydes (Scheme 2.16) [41, 42]. Similarly, Z-selective Peterson reactions of the in situ generated a-phosphoryl-a-(trimethylsilyl)allyl anion 104 with aldehydes or alkyl formates to afford the 2-dienylphosphonates 105 have been reported (Scheme 2.63) [168, 169]. These methods allow access to (Z)-alkenylphosphonates, whereas Wittig-Horner reactions give the thermodynamic ( )-alkenes almost exclusively. These excellent Z-selectivities can be rationalized in terms of the chelation control mechanism (see Section 2.2.2.3). 

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