Oxaphospholans

2-Oxaphospholans.—The stable phosphoranes (41) were obtained from ylides and epichlorohydrin.35 The formation of (41 R = H) from the action of base on the salt (42) supports a mechanism via the intermediate ylides (43). The crystalline cyclic 

2-Oxaphospholans.—The distillable oxyphosphoranes (48) have been obtained from methylenephosphoranes and oxiran, and their low-temperature and 

Methyl diphenylphosphinite and u-hydroxycinnamic acid gave the bicyclic acyloxy-phosphorane (52). This rearranged above its melting point to give the coumarin (54) and was hydrolysed rapidly to give the phosphine oxide (53). 

2-Oxaphospholans.—Full details have appeared of the reactions of the lactone and dione dimers of dimethylketen with a series of tervalent phosphorus esters and amides, and the postulated quinquecovalent intermediate (49) from the lactone dimer has been isolated in one case. Of potential mechanistic significance is the preferred migration of exocyclic substituents in the steps corresponding to (49) (50). 

The formation of a stable 1,2-oxaphospholan from the sodium salt of benzoin and triphenylvinylphosphonium bromide has been extended to substituted vinylphosphonium salts, diastereoisomers being obtained in some cases. 

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The reaction of diacetone alcohol 1 with alkyldichlorophosphines afforded 3-chloro-l,2-oxaphospholane-2-oxide 2. The latter undergo isomerization followed by dehydrochlorination to the corresponding 1,2-oxaphosphole derivatives 3 (Scheme 1) [29],... 

Secondary phosphines with a /3-hydroxyethyl substituent, obtained by addition of primary phosphines to a-oxides, easily undergo a reaction with ketones and aldehydes, giving 1,3-oxaphospholanes (6) [Eq. (4)] (72T2587). 

The spatial structure of 16 stereoisomers of 1,3-aza-, 1,3-thia-, and 1,3-oxaphospholanes was determined (75OMR470). H NMR spectra of several stereoisomers of phospholanes, containing N and O atoms in the 3-position to phosphorus, have been presented [78PS(4)59 83PS51], However, the conformational equilibrium was not studied (Fig. 2). 

Irradiations of l,3,2-dioxaphosph(V)oles in various solvents with and without sensitizers have also been described67. 2,2,2-Trimethoxy-4,5-dimethyl-1,3,2-dioxaphospho-lene (32) added acetone under photo-irradiation to yield the oxaphospholane 33 (equation 15)68. Using slightly damp acetone, the cyclic phosphate 34 is obtained. However it could be shown that the oxetane 35 is formed as an intermediate in the photocondensation... 

The reaction of oxaphospholanes 235 derived from 3-hydroxy-3-arylphosphonium salts 234 and DBU with paraformaldehyde yielded 4-aryl-6-methylene-l,3-dioxepanes 89 (Scheme 69) <2005BCJ2209>. 

Die Reaktion wurde besonders auf 2-Organo-5-oxo-1,2A5-oxaphospholan-2-oxide ange-wendet. So erhalt man aus dem 2-Ethyl-Derivat und 180-markiertem Wasser (2-Carboxy-ethyl)-ethyl-phosphinsdure107 ... 

Lthvl-4-methyl-5-oxo- l,2-oxaphospholan-2-oxid77 Zu 13,1 g(0,l mol) Dichlor-ethyl-phosphan tropft man unter Kohlendioxid-Schutzgas und Riihren 8,6 g (0,1 mol) 2-Methyl-acrylsaure. Nach 2 Stdn. bci 60° werden 50 ml Benzol und nochmals 8,6 g (0,1 mol) 2-Methyl-acrylsaurc zugegeben und weitere 3 Stdn. bei 58° gehalten. Nach Abziehen einer Mischung aus Benzol und 2-Methyl-acrylsiiure-chlorid wird i. Vak. destilliert Ausbeute 10,0 g (63°/,) Sdp. 9773 Torr (0,4 kPa). 

Methyl-5-oxo-1,2-oxaphospholan-2-o3rid383 Zu 10,2 g (0,11 mol) Acetanhydrid tropft man unter Riihren 18,89 g (0,1 mol) (2-Chlorcarbonyl-ethyl)-methyl-phosphinsaure-chlorid, erhitzt 1 Stde. auf 55°und destilliert Ausbeute 11,3 g (84%) Sdp. 149-15070,5 Torr (0,07 kPa). 

Dimethyl-2-isopropyliden-5-oxo-3,3,3-trimethoxy-1,325-oxaphospholan liefert beim Erwarmen auf 60° dimeres Dimethylketen71 ... 

Phosphinsaure Ethyl-[2-(3-nitro-anilinocarbonyl)-ethyl]- E2, 141 (aus 5-Oxo-l, 2-oxaphospholan-2-oxid-Der. + Amin)... 

A /l -phosphane oxide was also obtained when oxaphospholane 1 rearranged to ylide 2 in the presence of a ketone and afforded an alkene. ... 

In the second reaction type, the ene and yne functionalities are found in two different phosphorus substituents. These 1-alkynylphosphonates undergo facile Pd(OAc)2-LiCl-catalyzed cyclization to give oxaphospholanes in good yields (77-89%, Scheme 1.27) but with low stereoselectivity, ratios at the exo double bonds being approximately 60/40. ... 

Synthesis and reactions of oxaphospholanes using hydroxyalkylphosphonium salts 00YGK548. 

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