Benzannulation of heterocyclic frameworks by 1,1-carboboration pathways.

A small series of S- and N-heterocyclic 1,2-bis(trimethylsilylethynyl)arenes (2, 9, and 12) react with the strongly electrophilic borane B(C6F5)3 in consecutive 1,1-carboboration sequences to benzannulated heterocyclic systems. With this approach, highly substituted carbazole (6), benzothiophene (10), and quinoline (14) derivatives can be synthesized. While benzannulation occurs in all three cases, the reactions are quite different in detail. Finally, one-pot deborylation reactions lead to hydroxy-hetarenes, as demonstrated for the hydroxy-carbazole 7 and the hydroxy-benzothiophene 11.

Frustrated Lewis pair modification by 1,1-carboboration: disclosure of a phosphine oxide triggered nitrogen monoxide addition to an intramolecular P/B frustrated Lewis pair.

The vicinal frustrated Lewis pair (FLP) mes2P-CH2CH2-B(C6F5)2 (3) reacts with phenyl(trimethylsilyl)acetylene by 1,1-carboboration to give the extended C3-bridged FLP 6 featuring a substituted vinylborane subunit. The FLP 6 actively cleaves dihydrogen. The FLP 3 also undergoes a 1,1-carboboration reaction with diphenylphosphino(trimethylsilyl)acetylene to give the P/B/P FLP 11 that features a central unsaturated four-membered heterocyclic P/B FLP and a pendant CH2CH2-Pmes2 functional group. Compound 11 reacts with nitric oxide (NO) by oxidation of the pendant Pmes2 unit to the P(O)mes2 phosphine oxide and N,N-addition of the P/B FLP unit to NO to yield the persistent P/B/PO FLPNO aminoxyl radical 14. This reaction is initiated by P(O)mes2 formation and opening of the central Ph2P···B(C6F5)2 linkage triggered by the pendant CH2CH2-P(O)mes2 group.

Dibenzopentalenes from B(C6F5)3-induced cyclization reactions of 1,2-bis(phenylethynyl)benzenes.

'Lene' and mean: The strong Lewis acid B(C6F5)3 efficiently converts some bis(arylethynyl)benzenes into dibenzopentalenes through a series of Lewis acid induced cyclization reactions at room temperature. Thus the reaction has the potential to be useful in the synthesis of substituted dibenzopentalene derivatives which are difficult to make by conventional means.

1,1-Carboboration route to substituted naphthalenes.

1,2-Bis(alkynyl)benzene derivatives react with strongly electrophilic boranes to yield in boryl-functionalized bulky naphthalene derivatives by means of a sequence of 1,1-carboboration reactions. These substrates can be functionalized by transition metal catalyzed cross-coupling reactions.