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Glycosylidene Carbenes, Part 29 , Insertion into B−C and Al−C Bonds: Glycosylborinates, ‐boranes, and ‐alanes
Author(s) -
Wenger Wolfgang,
Vasella Andrea
Publication year - 2000
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/1522-2675(20000705)83:7<1542::aid-hlca1542>3.0.co;2-f
Subject(s) - chemistry , carbene , protonolysis , hydrogenolysis , anomer , hemiacetal , alkyl , stereochemistry , hydrolysis , diazirine , yield (engineering) , medicinal chemistry , catalysis , organic chemistry , materials science , metallurgy
Insertion of the glycosylidene carbenes derived from the diazirines 1 , 14 , and 15 into the B−alkyl bond of the B ‐alkyl‐9‐oxa‐10‐borabicyclo[3.3.2]decanes 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 glycosylborinates are stable under acidic, basic and thermal conditions. The unprotected glycosylborinate 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 BEt 3 , BBu 3 , and BPh 3 led to unstable glycosylboranes that were oxidised to yield the hemiacetals 29 (55%), 31 (45%), and 33 (48%), respectively, besides 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( i Bu) 3 and AlMe 3 to generate reactive glycosylalanes that were hydrolysed, yielding the C ‐glycosides 46 (21%) and 49 (30%), respectively, besides the glucals 48 (26%) and 51 (30%); deuteriolysis instead of protonolysis led to the monodeuterio analogues of 46 and 49 , respectively, which possess an equatorial 2 H‐atom at the anomeric center.