These fragmentations were accomplished thermally (110" in toluene). We later found that the fragmentations could be conducted at room temperature by subjecting the precursors to ultraviolet light (254 nm) [2], and we generated both alkyl metaphosphates and N,N-dimethylmetaphosphoramidate (Me2N-P02) by this method. Other studies have led to the generation of alkyl metathiophosphates [3]; applications of the 3-coordinate species for special phosphorylations have also been described [4]. We have continued to develop the chemistry of the 2,3-oxaphosphabicyclo[2.2.2]octene ring system, and we report in this paper some new observations on the synthesis and stereochemistry of the system, as well as on some kinetic studies of the thermal fragmentation that provide compelling proof that a free metaphosphate is indeed released. Additional proof for a free metaphosphatt, has come from the use of chiral P-alkoxy derivatives of the bridged ring system, which are useful in proving the planarity of the species, but also reveal that an oxy function properly placed may undergo anchimeric participation with the metaphosphate function.In Scheme 1 is outlined the general synthetic method used for the construction of the requisite ring system. Phosphole oxide intermediates are first generated and instantly trapped by Diels-Alder reaction with a maleimide derivative to give a product with the 7-phosphanorbornene framework. No other dienophile has yet been found to be superior 0 1991 VCH Publishei-s, Inc
Dehalogenation of R2NPC12 (R = isopropyl or cyclohexyl) with magnesium in tetrahydrofuran gives the corresponding cyclotetraphosphines (R2Ñ)4P4; the corresponding biphosphines (t-Pr2N)2P2X2 (X = Cl and Br) can be isolated from reactions of t'-Pr2NPX2 with more limited quantities of magnesium. Dehalogenations with magnesium of R2NPC12 derivatives having R2N groups smaller than diisopropylamino lead to redistribution of the dialkylamino groups giving (R2N)2P-P(NR2)2 (R2N = piperidine) or (R2N)3P (R2N = diethylamino or dimethylamino). Such redistribution reactions can be suppressed but not eliminated by using the homogenous dehalogenating agent (Me3Si)2Hg in hydrocarbon solvents. The steric bulk of the diisopropylamino groups in (i-Pr2N)4P4 reduces its chemical reactivity relative to other cyclotetraphosphines; thus (¿-Pr2N)4P4 is unreactive toward oxygen, carbon disulfide, potassium metal, and various metal carbonyls [e.g., Cr(CO)6, Mo(CO)6, and Fe2(CO)9] under conditions where other cyclotetraphosphines react with these reagents. However, the P4 ring in (i-Pr2N)4P4 is cleaved under mild conditions by hydrogen chloride as well as by bromine and iodine.Cyclopolyphosphines of the type R"P" having exocyclic phosphorus-carbon bonds are well-known.3,4 However,
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