Catalytic Hydroboration with Rhodium Complexes

Abstract

Cb,CH, 12&&H, 13 Degradation (or oxidation) of the phenyl group in the acetal 12, chemoselective reduction of the carboxylic acid 13 to the alcohol, and subsequent cyclization affords access also to the threo-configurated derivative of the apiose, an L-apio-D-furanose derivative. It is thus shown, by way of example, that this chiralic controlled photo-aldol reaction is suitable for the general synthesis of branched carbohydrates starting from "non-sugar building blocks".~'61 Experimental la: A solution of pyridine (13.5 g) and (-)-8-phenylmenthol (alcohol a) in toluene (100 mL) was added dropwise at 0-5'C to a solution of PhCO-COCI (20.2 g) in toluene (100 mL). After ca. 12 hours' stirring the reaction mixture was washed with 10% HCI, 5% NaHCO3, and water, then dried with MgSO.,, and finally evaporated to dryness. Subsequent recrystallization (three times, hexane-ether 6 : 1) of the residue furnished 22 g of the ester la (5l%), m.p. 90-91.5"C. It should be noted that, unless the alcohol a has been purified via its chloroacetic acid ester, a separation o f diastereomers is camed out during the recrystallization, since the (-)-8-phenylmenthol synthesized according to the method given in the literature"' contains up to 15% of an isomer.4a: A solution of la (16.4 g) and 2 (4.5 g) in anhydrous benzene (500 mL) was irradiated for 6 h with a T71822 (Hanau Heraeus) lamp in a falling-fitm apparatus. The solution was then evaporated, filtered over silica gel (CH2CIZ), and the residue remaining after the removal of solvent was dried.Yield 20.7 g (99%) of oxetane 4a, m.p. 73°C; [rr]g= -9.1 (c=0.98, EtOH).Since the volume of the irradiation vessel was ca. 1000 mL, up to 40 g of oxetane could be synthesized in one batch. Publication delayed at the authors' request German version: Angew. Chern. 97 (1985) 854 Solution, Part 4. We thank J. P. Jacobsen for his assistance. This work was supported by the Deutsche Forschungsgemeinschaft and the Fonds der Chemischen 1ndustrie.-Part 3: [la]. Angew. Chem. Int. Ed. Engl. 24 (1985) No. 10 0 VCH Verlagsgesellsehaft mbH. 0-6940 Weinheirn, 1985

Synthesis, Structure, and Catalytic Studies of Palladium and Platinum Bis-Sulfoxide Complexes

“…The catalytic version of this reaction has been most welldeveloped with rhodium catalysts. [47][48][49][50][51][52][53][54][55][56][57][58][59][60] There is very little in the current literature regarding the use of platinum in hydroboration reactions. There is only one example of catechol borane being used in the hydroboration of a terminal alkene with a platinum catalyst.…”

Metal Vinylidenes as Catalytic Species in Organic Reactions

“…Traditionally one has only had direct access to E-1-alkenylboranes by rhodium-catalyzed hydroboration of terminal alkynes using Wilkinson's catalyst [119] In order to explain the regio-and stereoselectivity, Miyaura proposed the mechanism shown in Scheme 108. The active catalyst (I) and the substrate form a vinylidene intermediate (II), a process that is consistent with deuterium labeling studies.…”

Iridium-catalyzed hydroboration of alkenes with pinacolborane

“…Representative metal complexes such as Rh(PPh 3 ) 3 Cl, 14 [Rh(nbd)(dppb)]BF 4 , 14 Cp*Sm(THF), 12 SmI 3 15 and Cp 2 ZrHCl 16 have been reported to yield terminal products (2) for both catecholborane and pinacolborane.…”