Phosphorus seven-membered rings

Axially chiral phosphoric acid 3 was chosen as a potential catalyst due to its unique characteristics (Fig. 2). (1) The phosphorus atom and its optically active ligand form a seven-membered ring which prevents free rotation around the P-0 bond and therefore fixes the conformation of Brpnsted acid 3. This structural feature cannot be found in analogous carboxylic or sulfonic acids. (2) Phosphate 3 with the appropriate acid ity should activate potential substrates via protonation and hence increase their electrophilicity. Subsequent attack of a nucleophile and related processes could result in the formation of enantioenriched products via steren-chemical communication between the cationic protonated substrate and the chiral phosphate anion. (3) Since the phosphoryl oxygen atom of Brpnsted acid 3 provides an additional Lewis basic site, chiral BINOL phosphate 3 might act as bifunctional catalyst. 

Methods to synthesize seven-membered rings containing phosphorus were previously described in CHEC-II(1996) <1996CHEC-II(9)947>. Herein, we report new synthetic approaches to these compounds that appeared in the literature after 1995. 

The mass spectra of a number of heterocyclic compounds have been reported. The fragmentation patterns of thiophosphoryl derivatives of phosphorinanes are sensitive to stereochemistry, thus for the series (95) facile loss of the HS radical is indicative of an axial PS bond. The seven-membered heterocycles (96 Ch = S, Se) undergo a remarkable migration of sulphur or selenium from phosphorus to carbon with ring cleavage. While exocyclic P-C bonds of five-and six-membered heterocycles in the phosphonic class may be readily cleaved with retention of the phosphorus ring system, the seven-membered ring (97) exhibits facile expulsion of a phosphorus radical. ... 

In this mechanism, a seven-membered ring is formed in the transition state and the (Me0)2P-0 unit serves as a leaving group. Path B is based on nucleophilic substitution at the phosphorus. It commences with the protonation of one methoxy group. This is the precondition for the subsequent positivation of the phosphorus atom. In the transition state, the formation of a thermodynamically stable six-membered ring is realized. 

Cascade reactions of benzodioxaphosphepine (17) with a-dicarbonyl compounds such as 9,10-phenantrenequinone (18) and dibenzoyl (19) gave other cage-like propeller derivatives (20) and (21) with five- and seven membered rings containing phosphorus-carbon bonds. They were also reported to be hydrolytically unstable (Scheme 4). ... 

Tetrahydrophosphinine oxide 166 reacts with dichlorocarbene under phase-transfer catalytic conditions giving 7,7-dichloro-1-methyl-3-phenyl-3-phosphabicyclo[4.1.0]heptane (167) in 71% yield. Heating the phosphabi-cyclo[4.1.0]heptane 167 at 220 °C makes the bicyclic ring opening and the simultaneous elimination of hydrogen chloride gives 4-chloro-3-methyl-l-phenyl-2,7-dihydrophosphepin 1-oxide (168), a seven-membered phosphorus heterocycle, in 67% yield (Scheme 54) [66]. 

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