Glycosylidene carbenes part 29 - Insertion into B-C and Al-C bonds: Glycosylborinates, -boranes, and -alanes

Insertion of the glycosylidene carbenes derived from the diazirines 1, 14 a nd 15 into the B-alkyl bond of the B-alkyl-9-oxa-10-borabicyclo[3.3.2]decan es 5, 6, and 7 yielded the stable glycosylborinates 8/9 (55%, 55:45), 10/11 (31%, 65:35), 12/13 (47%, 60:40), 16/17 (55%, 55:45), 18/19 (47%, 45:55), and 20/21 (31%, 30:70). Crystal-structure analysis of 17 and NOEs of 9 and 19 show that 17 9, and 19 adopt similar conformations. The glycosylborinate s are stable under acidic, basic and thermal conditions. The unprotected gl ycosylborinate 25 was obtained in 80% by hydrogenolysis of 12. Insertion of the glycosylidene carbene derived from the diazirine 1 into a B-C bond of BEt3, BBu3, and BPh3 led to unstable glycosylboranes that were oxidised to yield the hemiacetals 29 (55%), 31 (45%), and 33 (48%), respectively, besid es the glucals 30 (13%), 32 (20%), and 34 (20%), respectively. Insertion of the glycosylidene carbenes derived from 14 and 15 into a B - C bond of BEt 3 led exclusively to hemiacetals; only 15 yielding traces of the glucal 40 besides the hemiacetal 39. The glycosylidene carbene derived from 1 reacted with AL(Bu-1), and AlMe3 to generate reactive glycosylalanes that were hyd rolysed, yielding the C-glycosides 46 (21%) and 49 (30%), respectively besi des the glucals 48 (26%) and 51 (30%); deuteriolysis instead of protonolysi s led to the monodeuterio analogues of 46 and 49, respectively, which posse ss an equatorial H-2-atom at the anomeric center.