Through the Michaelis-Arbuzov-Kaehne Reaction

The scope of the Michaelis-Arbuzov reaction has been so widely examined that it is useful to consider separately the various aspects of the procedure, noting that, from the practical viewpoint, such reactions are carried out either by heating a mixture of reactants to a temperature sufficiently high to initiate and complete the reaction or by the addition of one reactant (usually the alkylating agent) to the second, pre-heated reactant. 

The use of trialkyl phosphites in the Michaelis-Arbuzov reaction has been so widespread during the decades following its discovery that it is almost impossible to select individual examples worthy of separate comment. Some examples of the preparation of benzylic phosphonic diesters may be noted these are of some interest since they are useful reactants in the Wadsworth-Emmons modification of the Wittig reaction, and are extensively used in the synthesis of alkenes It may also be noted that when the phosphite ester possesses different alkyl groups, some selectivity of reaction is possible.  

The use of acyclic phosphonite esters, R P(OR)2, to prepare esters of phosphinic acids, R R P(0)0R (R and R may, or may not, be identical) is not so widely exemplified, but it may again be noted that there are always two routes, theoretically, to a target compound, as for example, in the case of the l,4-phenylenebis(methylene)bisphosphinic esters 

It is perhaps not surprising that, should competition be possible between five-, six- and seven-membered rings in Michaelis-Arbuzov reactions, the six-membered ring tends to be retained at the expense of the other rings. Thus, the 2,7,8-trioxa-l-phosphabicyclo- 

Nevertheless, isolated seven-membered rings, as in the optically active phosphonites 22 (R = Me, or RR = CMe2), are also subject to ring opening when acted upon by the benzylic halides 4-YC6H4CH2X the products are the esters 23, which may be obtained with diastereoisomeric excesses ranging from 24% (X = I, Y = Me) to 99% (X = I, Y = CN, or NO2) no reaction occurs with X = Br and Y = CN or NO2, and the diastereoisomeric excesses for X = Br, Y = H or Me are 20-30%  

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