Alkylboronic preparation

Solution polymerization of VDE in fluorinated and fluorochlorinated hydrocarbons such as CEC-113 and initiated with organic peroxides (99), especially bis(perfluoropropionyl) peroxide (100), has been claimed. Radiation-induced polymerization of VDE has also been investigated (101,102). Alkylboron compounds activated by oxygen initiate VDE polymerization in water or organic solvents (103,104). Microwave-stimulated, low pressure plasma polymerization of VDE gives polymer film that is <10 pm thick (105). Highly regular PVDE polymer with minimized defect stmcture was synthesized and claimed (106). Perdeuterated PVDE has also been prepared and described (107). 

As in the Negishi reaction, various alkylboron reagents have also been successfully coupled with electrophile partners. Suzuki et al. coupled 1-bromo-l-phenylthioethene with 9-[2-(3-cyclohexenyl)ethyl]-9-BBN (27), prepared by a simple addition of 9-borabicyclo[3.3.1]nonane (9-BBN) to 4-vinyl-1-hexene (26), to furnish 4-(3-cyclohexenyl)-2-phenylthio-1-butene (28) in good yield [36],... 

One of the prominent synthetic protocols for the preparation of diazaborolines 323 involves the reaction of lithiated diamides 324 with boron halides and subsequent elimination of lithium halide salt. Another protocol involves synthesis via cyclocondensation of 1,2-diimines 325 with alkylboron halides to yield the diazaborolium salts 326 that undergo reduction with sodium amalgam yielding the diazaborolines 323 in high yield (Scheme 53) <2005EJI4715>. 

Hartwig and Chen136 showed that using photochemical activation of Cp Re(CO)3 with irradiation from a 450-W medium-pressure mercury lamp in the reaction of bis(pinacolato)diborane(4) in alkane in the presence of Cp Re(CO)3 (2.4—5.0 mol%) and CO (2 atm) produced the corresponding alkylboronates. Photochemical reaction of //-hexane with Cp Re(CO)2 (Bpin)2, prepared from Cp Re(CO)3 and pin2B2, led to the regiospecific formation of 1-borylpentane in quantitative yield (Scheme 46). 

A small-scale procedure, based on the reaction of bis(trifluoroethyl) alkylboronates with diphenylprolinol (eq 7) was reported for the preparation of the B-ethyl- (9b) and B-butyl-(9c) oxazaborolidines. The bis(trifluoroethyl) alkylboronates were prepared from the disproportionation of tris(trifluoroethyl) borate and the corresponding trialkylborane. Since trimethylb-orane is not commercially available, this procedure is not applicable for the preparation of B-methyloxazaborolidine (9a). 

Alkylboronic acid esters, RB(OR )2, can be prepared by addition of an excess of an alcohol to the reaction abovc. ... 

Attempts to isolate clathrochelate technetium (III) tris-dioxi-mates via template cross-linking three dioxime molecules with alkylboronic acid have not been successful. Only semiclathrochelate TcNx(HNx)2(BR2)Hal and TcDm(HDm)2(BR2)Hal complexes (where HaF is Cr, Br R is CH3 and A1-C4H9) were prepared [87, 88],... 

Brown and coworkers have described an alternative synthesis of chiral alkylboronic esters. In this synthesis prochiral alkenes are hydroborated with monoisopinocamphenylborane to yield isopinocam-phenylalkylboranes which are then readily transformed to chiral alkyllraronic esters (Scheme 39). Homologation with dichloromethyllithium, followed by reduction with potassium triisopropoxyborohy-dride (KIPBH) and oxidation, finely yields B-chiral alcohols (Scheme 40). These alcohols are not easily prepared by other methods. Aldehydes can be prepared by homologation from chiral alkylboronic esters with LiCH(OMe)SPh and oxidation (Scheme 41). ... 

Dialkylzincs can be prepared by transmetallation of zinc sails with alkylating reagents of the main group elements. Transmetallation of Me2Zn[23] with alkylborons is a particularly useful route to dialkylzincs (eq (12)) [24]. Since alkylborons are readily accessible by well documented hydroboration reactions of alkenes, a wide variety of dialkylzincs can be synthesized by this route. Dialkylzincs can be also obtained by the reaction of Et Zn [21] with olefins in the presence of a catalytic amount of Ni(acac) (eq(13))[25], ... 

Although lithium alkyls, owing to higher reactivity, show a tendency to form dialkylated products , they can also be used to prepare certain alkylboronic esters ... 

The reactions of dialkyl- or diarylborinic acid esters and alkylboronic acid esters with organolithium, Mg or Al compounds may serve to prepare unsymmetrical BRjR and BArjAr organoboranes " Synthesis of such organoboranes usually proceeds without complications ... 

Instead of n-C4H9B(OH)a, (n-C HgBOlg may be treated with BF3, in which case B2O3 is produced along with the n-C HgBFg. The procedure described is general and may be used for the preparation of all alkylboron dt uorides. Substitution of BCl 3 for BF 3 yields the alkylboron dichlorides. 

Synthetic intermediate of the cytotoxic ketide callystatin A 115 was prepared by coupling the alkylboronate 113 with the alkenyl iodide 114. The coupling product 115 was obtained in 73 % yield when PdCl2(dppf), AsPh3, and CS2CO3 were used in aq. DMF [90]. 

The a,ft)-asymmetric polymers are available by the combination of the functional initiator and functional terminator methods. By the rational combination of haloboration-initiation and capping techniques, a series of a.w-asymmetrically functionalized PlBs have been prepared [139, 140]. Polymers prepared by haloboration-initiation invariably carry an alkylboron head group [42, 141, 142], which can easily be converted into a primary hydroxy [141] or a secondary amine group [139, 140]. To functionalize the (W-living ends, the functionalization strategy shown in Scheme 26.2 is applicable and has been used to incorporate methoxycarbonyl groups as w-functionahty [143]. 

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