Iridium-Catalyzed Cyclative Indenylation and Dienylation through Sequential B(4)–C Bond Formation, Cyclization, and Elimination from o-Carboranes and Propargyl Alcohols

Abstract

Described herein is the first iridium-catalyzed cyclative indenylation through sequential B(4)–C and intramolecular C–C bond formation from o-carboranes and propargyl alcohols, leading to the formation of B(4)-indenylated o-carboranes with excellent regioselectivity via direct B–H activation. Moreover, the iridium-catalyzed regioselective 1,3-dienylation has been accessed through sequential B–H activation, dehydration, and decarboxylation, producing B(4)-dienylated o-carboranes.

Selective B(5,8,9)-Triarylation Reaction of o-Carboranes through Determination of the Order of Introduction of Aryl Groups into B(4)-Acylamino-o-carboranes

“…8i As a continuation of these studies, we have also reported B(4)-indenylation and B(4)-1,3-dienylation, 9 and we next focused on the iterative and selective arylation of o-carborane due to the significance of arylated o-carboranes. To date, B (9,12)-diarylated o-carboranes have been indirectly accessed through Pd-catalyzed cross-coupling reactions of B(9,12)-diiodo-o-carboranes with arylmagnesium bromides (Scheme 1a). 10 After deboronation of carborane using a base, the boronation reaction of nidocarboranes with PhBCl 2 yielded B(3)-arylated o-carboranes (a).…”

“…After noncatalytic works leading to vertex-selective functionalization of boron clusters, recently, a variety of transition metal-catalyzed functionalizations of o -carborane using the assistance of a carboxylic acid as a directing group have been reported: B(4)-heteroarylation, B(4)-alkenylation, B(4)-alkynylation, B(4)-hydroxylation, B(4)-amidation, − B(4)-amination, and B(4)-halogenation . As a continuation of these studies, we have also reported B(4)-indenylation and B(4)-1,3-dienylation, and we next focused on the iterative and selective arylation of o -carborane due to the significance of arylated o -carboranes. To date, B­(9,12)-diarylated o -carboranes have been indirectly accessed through Pd-catalyzed cross-coupling reactions of B­(9,12)-diiodo -o -carboranes with arylmagnesium bromides (Scheme a) .…”

Direct and Regioselective Palladium(II)-Catalyzed B(4)–H Monoacyloxylation and B(4,5)–H Diacetoxylation of o-Carborane Acids with Phenyliodonium Dicarboxylates

“…Consequently, the development of a mild and efficient method for the direct and regioselective construction of a B–O bond via a B–H functionalization is still a challenging subject . In a continuation with our studies directed toward the development of a transition-metal-catalyzed functionalization of o -carboranes and our ongoing interest in the synthesis of o -carboranes having B cage –heteroatom bonds, we demonstrate herein a direct and regioseletive Pd-catalyzed B(4)-monoacyloxylation and B­(4,5)-diacetoxylation reaction of o -carborane acids with phenyliodonium dicarboxylates (Scheme f).…”

Synthesis of Indolyl-Tethered Spiro[cyclobutane-1,1′-indenes] through Cascade Reactions of 1-(Pyridin-2-yl)-1H-indoles with Alkynyl Cyclobutanols

“…From the resulting mixture, however, the proposed enonyl-appended indole product as shown in Scheme b was not found. Instead, 1-(pyridin-2-yl)-2-(spiro­[cyclobutane-1,1′-inden]-2′-yl)-1 H -indole ( 3a ) was formed in 65% yield (Scheme c and Table , entry 1). , Although our initially envisioned product was not obtained, we realized that the unexpected formation of 3a might be more valuable for the following reasons. First, this reaction disclosed an unrevealed reaction pattern of alkynyl cyclobutanol as a coupling partner featuring spirocyclization and preservation of the cyclobutyl ring.…”

“…On the basis of the experimental results described above and previous studies, , a plausible pathway accounting for the formation of 3a is deduced rationally in Scheme . Initially, an Ir­(III)-catalyzed o -C–H bond activation occurs with 1a to form intermediate I .…”