Allene phosphonates

Dipole Homents and Kerr Effect. - The structures of two conformers of ethyldifluorophosphane have been determined using a combination of dipole moments and microwave spectroscopy.227 Dipole moments have been used to study the different tuist angles of allenic phosphonates (81),228 and also to deduce the stereochemistry of 1,3,2,5-dioxaboraphosphorinane.22 ... 

The nucleophilic addition of 1,2-allenic phosphonates with EtOH followed by hydrolysis leads to the formation of /8-ketophosphonates (Scheme 10.75) [83a]. Intramolecular nucleophilic addition of a hydroxyl group with 1,2-allenic phosphonate was also observed to produce 2,3-dihydrofurans [83b]. 

Scheme 18.36 Synthesis of the allenic phosphonate 112 by [2,3]-sigmatropic rearrangement [110].

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. ... 

Reactions between the allenic phosphonates (170) and the methylene amido-phosphites (171 R = Ph) initially afford unstable phospholens (172) which can be hydrolysed to (173) and ultimately to (174). When (171 R = NEtj) is employed, another reaction pathway is followed with elimination of diethyl-amine giving [(azaphosphorin-3-yl)methyl]phosphonates (175), which are hydrolysable to (176), The product from (170 R = H) and (171 R = NEt2) is 1-dimethoxyphosphinylpropyne. This last, as well as other esters of (1-pro-pyne)phosphonic acid, reacts further with (171 R = NEtj) to give (177) and thence (178). ... 

Two novel reaction sequences have been noted for allenephosphonic diesters. The cour.se of the reaction between the [l-(methoxymethyl)allene]phosphonic diesters (468)... 

Five- to eight-membered ring oxacycles are readily prepared by treating aUene sulfones and allene phosphonates bearing co-hydroxyl side chains with t-BuOK in r-BuOH at slightly elevated temperatures. The yields obtained with the hydroxyphosphonates are shown in eq 62. ... 

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