Organoboranes reacting with

Organoboranes react with propargylic carbonates. Usually, addition of a base is essential for the Pd-catalyzed reactions of organoboranes, but the reaction with propargylic carbonates proceeds without addition of the base, because methoxide is generated in situ from carbonates. For example, the 1,2,4-triene 80 is prepared by the reaction of alkenylborane under neutral conditions[36]. 

Organoboranes react with a mixture of aqueous NH3 and NaOCl to produce primary amines. It is likely that the actual reagent is chloramine NH2CI. Chloramine itself,hydroxylamine-O-sulfonic acid in diglyme, and trimethyl-silyl azide " also give the reaction. Since the boranes can be prepared by the hydroboration of alkenes (15-16), this is an indirect method for the addition of NH3 to a double bond with anti-Markovnikov orientation. Secondary amines can be prepared by the treatment of alkyl- or aryldichloroboranes or dialkylchlorobor-anes with alkyl or aryl azides. 

Organoboranes react with ethyl 4-nitrobenzenesulphonyloxycarbamate under basic two-phase conditions in the presence of benzyltriethylammonium chloride or Aliquat to yield ethyl (V-alkylcarbamates [38]. The reaction probably proceeds via the initial formation of the nitrene, which reacts with the borane to form a B -N+ zwitterion. Subsequent rearrangement and solvolysis leads to the product. Aliquat is the better catalyst for the higher-molecular-weight boranes. 

Organoboranes react with a mixture of aqueous NH3 and NaOCl to produce primary amines.358 It is likely that the actual reagent is chloramine NH2C1. Chloramine itself,359... 

Organoboranes react with bromine to form brominated boranes,l44 but they also react with brominated substrates. a-Bromo esters, for example, react with organoboranes to give coupling products if a base is added to the bromination reaction.Adding a base suppresses radical bromination, allowing an ionic reaction to... 

Suzuki and co-workers found that aryl triflates react with arylboronic acids [ArB(OH)2], in the presence of a palladium catalyst, to give biaryls in a reaction that is now known as Suzuki coupling.269 Even hindered boronic acids give good yields of the coupled product.2 0 Organoboranes, react with aryl triflates under these conditions as well. In a simple example, boronic acid 426 reacted with 3-bromopyridine in the presence of Pd(PPh3)4 to give a 90% yield of the biaryl 427.2 2... 

Organoboranes react with ethyl y-bromocrotonate (90) to give the Py-unsaturated esters (91), providing a convenient four-carbon homologation procedure. ... 

Fluorinated organoboranes reacted with internal alkynes through 1,2-alkyl/aryl migration to afford tetrasubstituted alkenes bearing a boron atom (Scheme 1.68) [89]. In a formal sense, one substituent on the alkyne migrated to another alkyne carbon to result in a vinylidene, which was inserted into the C-B bond. 

Organoboranes undergo transmetallation. 1-Hexenylboronic acid (438) reacts with methyl acrylate via the transmetallation with Pd(OAc)2, giving methyl 2,4-nonadienoate (439)[399], The ( )-alkenylboranes 440, prepared by the hydroboration of terminal alkynes, are converted into the alkylated ( )-alkenes 441 by treatment with an equivalent amount of Pd(OAc)2 and triethylamine[400]. The ( )-octenylborane 442 reacts with CO in MeOH in the... 

AUylic organoboranes react via cyclic transition states not only with aldehydes and ketones, but also with alkynes, aHenes, and electron-rich or strained alkenes. Bicyclic stmctures, which can be further transformed into boraadamantanes, are obtained from triaHyl- or tricrotylborane and alkynes (323,438,439). 

Sodium borobydride reacts with Lewis acids in nonprotic solvents to yield diborane [19287-45-7] 2 6 which can then be used to generate other useful organoboranes such as amine boranes, alkyl boranes, and boron hydride clusters. 

P-chlorocarbamates which can be converted to aziridines and alkyloxazoUdones (93,115). A/-Chloro-A/-sodiourethane reacts with organoboranes forming A/-alkylcarbamates (114), and with olefins, catalyzed by Os, forming vicinal hydroxy carbamates (116). 

Organoboranes can also be used to construct carbon-carbon bonds by several other types of reactions that involve migration of a boron substituent to carbon. One such reaction involves a-halo carbonyl compounds.20 For example, ethyl bromoac-etate reacts with trialkylboranes in the presence of base to give alkylated acetic acid derivatives in excellent yield. The reaction is most efficiently carried out with a 9-BBN derivative. These reactions can also be effected with (3-alkenyl derivatives of 9-BBN to give (3,y-unsaturated esters.21... 

Organoboranes R2BH or R3B (R = C10H21, cyclohexyl or cyclooctyl etc.) react with hydroxylamine O-sulphonic acid or its mesityl derivative or with chloramine to form primary amines RNH2100 101. 

Hydroboration of alkenes generates organoboranes, which react with sodium azide in the presence of an aqueous acid to give primary amines (equation 58). Thus 1-nonene... 

While die above reactions represent only a small fraction of die reactions known for palladium, they form the basis of a powerful methodology for building carbon structures. Several variations have been developed which utilize certain types of reactants and give particular types of products. All diese variations, however, contain a common theme. In each case an electron-deficient reagent (e.g., a vinyl halide or aromatic triflate) reacts with an election-rich reagent (e.g., an alkene, an organoborane, or an organotin) witii the formation of a new carbon-carbon bond. In that sense diese reactions are related to die reactions between carbon nucleophiles and carbon electrophiles discussed previously in diis chapter. They are quite different, however, because diey proceed only in the presence of Pd(0). In fact they proceed only in die coordination sphere of Pd(0). The ability of Pd(0) to catalyze diese reactions is nearly unique We will now examine some of die more common processes. 

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