Glycosylidene Carbenes. Part 21. Synthesis of N‐tosylglycono‐1,4‐lactone hydrazones as precursors of glycofuranosylidene carbenes

Abstract

The W -(glycofuranosylidene)toluene-4-sulfonohydrazides 5 and 10 (Scheme I ) were prepared in good yields by oxidation (1,3-dibromo-5,5-dimethylhydantoin/Et3N) of the W -glycosyltoluene-4-sulfonohydrazides 4 and 9, which were obtained from 2,3,5-tri-0-benzyl-o-ribose (3) and 2,3,5-tri-O-benzyI-o-arabinos.e (8), respectively, and toluene-4-sulfonohydrazide. The analogous naphthalene-2-sulfonohydrazides 7 and 12 were similarly prepared from 3 and 8 via 6 and 11. Photolysis in the presence of phenol of the sodium salt 15 (Scheme 2), best generated in situ, yielded the anomeric glycosides 16, some 5, and traces of the glycosides ( Introduction. -Glycopyranosylidene carbenes, known reactive intermediates [ 11, are best generated from diazirines, such as 1, under mild thermal and photochemical conditions [2]. They are also formed from the alkali salts of N'-glycosylidenesulfonohydrazides, such as 2 [3] [4], or (in low yields) from diazides under photochemical conditions [5]. N' -(Glycopyranosylidene)sulfonohydrazides are more readily prepared than the corresponding diazirines and are more stable. Their salts react similarly to diazirines in forming glycosides with phenols [&9] and cyclopropanes with electron-deficient alkenes [3] [9] [lo]. Thermolysis of N' -(glycopyranosylidene)sulfonohydrazides, however, also generates sulfinates, and this results in the formation of additional by-products [I 11 [12].

Catalytic Stereoselective 1,2-cis-Furanosylations Enabled by Enynal-Derived Copper Carbenes

“…The sodium salts of these N-tosylhydrazones under photochemical conditions generate the corresponding anomeric carbenes, which undergo an O−H insertion reaction with alcohols to form O-glycosides (Figure 1b). 10 However, the glycosylidene carbenes generated from the sodium salts of N-tosylhydrazones require an excess of alcohol acceptors to synthesize O-glycosides. Additionally, product yields in these transformations were remarkably low, and the scope was found to be very limited.…”

“…Because of the instability of diazirines, they then employed the anomeric N -tosylhydrazone donors, which are benchtop stable carbene precursors. The sodium salts of these N -tosylhydrazones under photochemical conditions generate the corresponding anomeric carbenes, which undergo an O–H insertion reaction with alcohols to form O -glycosides (Figure b) . However, the glycosylidene carbenes generated from the sodium salts of N -tosylhydrazones require an excess of alcohol acceptors to synthesize O -glycosides.…”

Glycosylidene Carbenes. Part 24 Reactivity modulation by protecting groups of the addition of glycosylidene carbenes to electron‐rich alkenes

“…-The nucleophilic character of glycosylidene carbenes has been evidenced, among others, by their reaction with electron-poor alkenes (for reviews, see . Thus, glycosylidene carbenes derived from the diazirines 1 [ 5 ] , 2 [ 6 ] , and 3 [7], and from the 4-toluenesulfonohydrazide sodium salts 4 [8] and 5 [9] add readily to electronpoor alkenes, leading to spirocyclopropanes. Yields of the products derived from the pivaloylated diazirine 1 were higher than those obtained from the benzylated diazirine 2, showing that the nature of the protecting groups influences the (nucleophilic) reactivity of these alkoxycarbenes 2).…”