Phosphorus hydrides atomic carbon

Intermediates such as 224 resulting from the nudeophilic addition of C,H-acidic compounds to allenyl ketones such as 222 do not only yield simple addition products such as 225 by proton transfer (Scheme 7.34) [259]. If the C,H-acidic compound contains at least one carbonyl group, a ring dosure is also possible to give pyran derivatives such as 226. The reaction of a similar allenyl ketone with dimethyl mal-onate, methyl acetoacetate or methyl cyanoacetate leads to a-pyrones by an analogous route however, the yields are low (20-32%) [260], The formation of oxaphos-pholenes 229 from ketones 227 and trivalent phosphorus compounds 228 can similarly be explained by nucleophilic attack at the central carbon atom of the allene followed by a second attack of the oxygen atom of the ketone at the phosphorus atom [261, 262], Treatment of the allenic ester 230 with copper(I) chloride and tributyltin hydride in N-methylpyrrolidone (NMP) affords the cephalosporin derivative 232 [263], The authors postulated a Michael addition of copper(I) hydride to the electron-... 

The phosphine 1-(1,2-C2BxoHii)P(CHs)2 was prepared and reacted with an iridium (I) complex, as shown in Fig. 27. Spectroscopic evidence strongly supported the view that the complexed Ir(I) had inserted into a B—H bond with the formation of an iridium-boron bond and an iridium-hydride link (58). Specific deuterium labels attached to the carborane moiety of the phosphine clearly proved this point. Thus, the B-H vertices of the icosahedral carborane group that are nearest the carbon atom bearing phosphorus were shown to be involved, although a distinction could not be made between the 3,6 or 4,5 sets of BH groups. 

An expeditious and highly diastereoselective synthesis of (Z)-2-alkylsulfenyl (or 2-cyano) -2,4-diarylthietanes 53 has been reported by nucleophile (CN, RS") induced cyclization of the corresponding O,O-diethyl 5-(l,3-diaryl-3-oxopropyl) phosphorodithionates under microwave irradiation in solvent free conditions <02S1502>. This reductive cyclization can be considered to be induced by the attack of a hydride ion on the carbonyl carbon of the Michael adduct precursor to give an alkoxide ion, which attacks the phosphorus atom intramolecularly. 

The synthesis of polyphosphines containing combinations of primary, secondary, and tertiary phosphorus atoms by the base-catalysed addition of P—H across the carbon-carbon double bond of vinyl phosphonates, followed by reduetion with lithium aluminium hydride, has again been described. The preparation of I,2-bis(phosphino)ethane from the bis-phosphonate (17) by reduction with lithium aluminium hydride has been reported in detail. ... 

The hydrogen atoms on the carbon attached to the resulting phosphorus cation are somewhat acidic because they are adjacent to a positive charge, a significant electron-withdrawing group. Thus, treatment of the phosphonium salt with a strong base, such as butyUithium in THE or sodium hydride in DMSO, removes one of these protons and produces the yUde. 

The hydrogen atoms of the two CH groups are acidic, in contrast to those of the BH groups, which are hydridic. Therefore, selective functionalization of the carbon atoms is possible by electrophilic substitution or deprotonation with strong bases followed by subsequent reaction with electrophiles. However, the steric bulk of the clusters requires appropriate reactivity of the electrophile to obtain the desired product in acceptable yields. Phosphorus-containing compounds such as halophosphines are suitable for this type of functionalization of carboranes. In 1963, the first reaction with phosphines was described and until today it has ranained the method of choice for phosphorus functionalization of carboranes. 

---