K. Praveen Kumar

Direct synthesis of α-substituted phosphonates

The a-substituted phosphonates (OCH2CMe2CH2O)P(O)CH(X)(Ar) [X=Cl, OMe, NMe2 and OSiMe3], useful precursors for Horner–Wadsworth–Emmons reactions, are readily prepared by treating (OCH2CMe2CH2O)PX with an aromatic aldehyde. In the reaction of (OCH2CMe2CH2O)PCl with furfuraldehyde and cinnamaldehyde, the 5-chlorofurfurylphosphonate (OCH2CMe2CH2O)P(O)CH2(5-Cl-C4H2O) and the g-chlorophosphonate (OCH2CMe2CH2O)P(O)CH CH-CH(Cl)Ph, respectively, are formed in good yields.

An easy access to trisubstituted vinyl chlorides and improved synthesis of chloro/bromostilbenes

The α-chlorophosphonates (OCH2CMe2CH2O)P(O)CHCl-C6H4-4-R [R=H (4), Me (5), OMe (6)], which are now readily accessible, react with ketones R′C(O)R″ in the presence of NaH (without recourse to the more expensive t-BuLi) to afford trisubstituted vinyl halides R′C(R″)=CCl(C6H4-4-R) in good yields. The corresponding α-bromophosphonates [R=H (7), Me (8)] failed to react with ketones and gave the symmetrical acetylenes 4-R-C6H4-CC-C6H4-4-R as isolable products in low yield. We have found that K2CO3 in refluxing xylene is a good base for the synthesis of chlorostilbenes; using this base the bromostilbenes ArCH=CBr(C6H4-4-R) can be prepared in significantly higher yields than by using NaH. The stereochemistry of two of the trisubstituted vinyl chlorides is unambiguously proven by X-ray structure determination. Thus for (Cl)PhC=CPh(Me), the isomer with the upfield NMR shift for the CH3 protons and for (Cl)PhC=C(Ph)(C6H4-4-Me), the isomer with the downfield NMR shift for the -C6H4-4-CH3 protons have Z stereochemistry.

Swarm intelligence based Resource Allocation Algorithm for cognitive radio network

In this paper, we propose a Swarm Intelligence based Resource Allocation Algorithm (SIRAA) for optimum allocation of available spectrum holes to cognitive radio users. Usage statistics reveal that large portion of the spectrum are under utilized due to stringent licensing policy. Spectrum utilization ranges from only 15% to 85% with a high variance in both temporal and spatial domain. Due to the inefficiency in the spectrum usage and increase in the access to the available limited spectrum in recent years, there is a need to access the existing wireless spectrum opportunistically. This new networking paradigm is referred as Cognitive radio networks. We used existing bidding strategy to allocate channels to cognitive radio users. A cognitive radio sends bid values (the bid value is a function of bandwidth requirement, bit error rate, possible interference, user type etc.) for every available spectrum holes to the base station. The base station allocates the spectrum band to the cognitive user by maximizing the totald bid value received from all cognitive users. We consider four different cases of allocation such that each cognitive user (i) will get exactly one channel (ii) will get channels in a proportionate manner (iii) will get at least k number of channels and (iv) will get at least k1 and at most k2 number of channels. We proposed a binary particle swarm optimization (PSO) technique to find an optimum allocation of channels to all cognitive users for all four cases. We compared our simulation results with traditional Hungarian method wherever the later is used to verify in some feasible cases.

THE REACTION OF CHLOROPHOSPHATES WITH STRONG BASES : SYNTHESIS AND CHARACTERIZATION OF THE PHOSPHONATE SALTS

Abstract The reaction of (OCH 2 CMe 2 CH 2 O)P(O)Cl ( 1 )with 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) afforded the phosphonate salt [(OCH 2 CMe 2 CH 2 O)P(O)(DBU)] + [Cl] ( 3 ) − ; the X ray structure of this compound as a hydrate shows that the C-6 (labeled as Cl in Fig.1) of the DBU is connected to the phosphorus. In an analogous manner the eight-membered ring compound {CH 2 (4-Me-2- t -Bu-C 6 H 2 O) 2 }P(O)Cl ( 2 ) also afforded a phosphonate salt along with the pyrophosphate [{CH 2 (4-Me-2- t -Bu-C 6 H 2 O) 2 }P(O)] 2 O ( 5 ). By contrast, in the reaction of 1 with 1,5-Diazabicyclo[4.3.0]non-5-ene (DBN), N-methyl imidazole or 4-dimethylaminopyridine no phosphonate salt was observed; the pyrophosphate was found to be the end product and could be isolated.

Oxidative addition reactions of cyclodiphosph(III)azanes

The ansa compound {[t-BuN)P]2[O-6-t-Bu-4-Me-C6H2]2CH2} (2) reacts with two mole equivalents of selenium to afford the bis(seleno) compound {[t-BuN)P(Se)]2[O-6-t-Bu-4-Me-C6H2]2CH2} (3); under analogous conditions sulfur gives the P(III)-N-P(V) derivative {[(t-BuN)PN(t-Bu)P(S)][O-6-t-Bu-4-Me-C6H2]2CH2} (4). These reactions are compared with those using [(ArO)PN(t-Bu)]2 (5) and the macrocycle {[t-BuN-P]2(OCH2CMe2CH2O)}2(6).

Formation of phosphonates and pyrophosphates in the reactions of chlorophosphate esters with strong organic bases

The compounds S(6-t-Bu-4-Me-C6H2O)2P(O)Cl (1), CH2(6-t-Bu-4-Me-C6H2O)2P(O)Cl (2) and (2,2′-C20H12O2)P(O)Cl (3) react with diazabicycloundecene (DBU) to give rise to, predominantly, the phosphonate compounds [S(6-t-Bu-4-Me-C6H6O)2P(O)(DBU)]+[Cl]− (4), [CH2(6-t-Bu-4-Me-C6H2O)2P(O) (DBU)]+[Cl]− (5) and [(2,2′-C20Hi2O2)P(0)(DBU)]+[Cl]- (6). The first two compounds could be isolated in the pure state. In analogous reactions of 1 and 2 with diazabicyclononene (DBN) or N-methyl imidazole, only the pyrophosphates [S(6-t-Bu-4-Me-C6H2O)2P(O)]2O (7) and [CH2(6-t-Bu-4-Me-C6H2O)2P(O)]2O (8) could be isolated, although the reaction mixture showed several other compounds in the phosphorus NMR. A possible pathway for the formation of phosphonate salts is proposed. The X-ray crystal structures of4,7 and8 are also discussed.

Unusual products in the reactions of phosphorus(III) compounds with N=N, C≡C or conjugated double-bonded systems

The diversity of products in the reaction of diethyl azodicarboxylate (DEAD)/diisopropyl azodicarboxylate (DIAD) and activated acetylenes with PIII compounds bearing oxygen or nitrogen substituents is discussed. New findings that are useful in understanding the nature of intermediates involved in the Mitsunobu reaction are highlighted. X-ray structures of two new compounds (2-t-Bu-4-MeC6H3O)P (μ-N-t-Bu)2P+[(NH-t-Bu)N[(CO2]-i-Pr)(HNCO2-i-Pr)]](Cl-)(2-t-Bu-4-MeC6H3OH)(23)and [CH2(6-t-Bu-4-Me-C6H2O)2P(O)C(CO2Me)C-(CO2Me)CClNC(O)Cl] (33) are also reported. The structure of23 is close to one of the intermediates proposed in the Mitsunobu reaction.