Phosphorane, thermolysis

In 1981, Appel et al. postulated the transient formation of the (diphenyl-phosphino)(trimethylsilyl)carbene 2e to explain the formation of the phos-phaalkene 4e, in the thermolysis of the P-chloromethylene phosphorane 3e.29 At that time, the authors did not recognize the carbene character of 2e and simply named the intermediate a A5-phosphaalkyne. 

Endocyclic P=N bonds tend to promote dimerization (Scheme 34) the phosphazane 132 is formed203 from the precursor 132a, and even if 134a is the result of the thermolysis of the phosphorane 133, as proved by the possibility of trapping it with a C=0 bond204, the product isolated is the dimer 134. 

The (Z)-isomers are prepared by a nonstereoselective Wittig reaction of the phosphorane 5 with aldehydes. On thermolysis of the resulting (E)/(Z) mixture, (E)-4 is converted into a dimer, and (Z)-4 is unchanged and easily separated from the dimer. 

Application of the Wittig route through thermolysis of phosphorane 372 yields the trinem analogue 373 in low to moderate yield (Equation 49) <1996BML525>. 

BML525, 1996BML2589>. The phosphorane may be isolated and used as the starting material in this final step. Thus, the triprotected phosphorane 384 was first desilylated and the resulting dihydroxy phosphorane was cyclized by thermolysis in toluene solution to yield 385 <1998H(48)2287>. 

Thermolysis of ()) -cyclopentadienyl)bis(neopentyl)(tri-methylphosphine)vanadium(I) (82) in the presence of 1,2-bis(dimethylphosphuio)ethane leads to the formation of the Schrock-type see Schrock-type Carbene Complexes) alkylidene vanadium complex (83), which is supported by X-ray crystallographic analysis (Scheme 45). " The imido vanadium complex (84) is converted to the corresponding alkylidene complex (86) on treatment with ben-zylidene(triphenyl)phosphorane (85) via substitution of the phosphine ligand (Scheme 46). ... 

Reductions of certain (acylalkylidene)phosphoranes with Zn-HOAc and conversion of (acylalkoxycar-bonylmethylene)phosphoranes to P-keto esters by a thermolysis route have been reported, but gave poor results with (acylethoxycarbonylmethylene)phosphoranes. The desired reductive removal of triphe-nylphosphine may be achieved in this case with excess Al-Hg in wet THF, with periodic addition of acids (equation 18). ... 

Studies of the oxaphosphorylation properties of diethoxytriphenyl-phosphorane (23) have been extended to include methyl a-D-glucopyranoside (24) which affords two isomeric dioxaphospholanes (25 and 26). Thermolysis of these phosphoranes in DMF at 40°C in the presence of LiBr, afibrds the allop3n anoside (27) in a regiospecific reaction whereas thermolysis in the absence of LiBr... 

The yellow crystalline solid is analytically pure (>95% by NMR and HPLC analysis), mp 124-127°C. We have found that the yield of the acetylenes can be adversely affected by small amounts of impurities in the a-acylmethylene-phosphoranes and prefer to recrystallize the phosphoranes prior to thermolysis. The yield from the recrystallization step Is greater than 95%. 

The azepino-indole (600 E = COjMe) is produced by thermolysis of methyl 2-azidodiphenylmethane4 -carboxylate, N3C6H4CH2C6H4C02Me. Treatment of the pyrrolo-azepine (601) with benzoylmethylenetriphenyl-phosphorane, PhCOCH=PPh3, yields the bridged compound (602) by successive Michael addition and intramolecular Wittig reaction The imidazo-azepine (604) is formed from (603) by ring-expansion with diazomethane.Addition of dimethyl acetylenedicarboxylate to the cyclo-... 

Pure (Z)-l,3-disubstituted 1,3-dienes can be obtained by Wittig reaction of the suitably substituted allylic phosphorane (31) followed by thermolysis which causes dimerization of only the ( )-isomer (Scheme 5). A variety of methods, including... 

The first example of a phosphorane containing two oxaphosphetane rings (52) has been synthesised by Kawashima and X-ray crystallography supported by multinuclear nmr indicate a distorted tbp configuration with the oxygen atoms apical as expected. Thermolysis of the phosphorane (in dg toluene) at 190 C in a sealed tube was complete after 24h and gave quantitative yields of the alkene (53) and the vinylphosphinic acid (55) via (54).21... 

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