The title compounds are α-amino acids whose nitrogen atoms are enclosed within 4,5-disubstituted, six-membered cyclic hydroxamates and they are of interest as potential β-lactam surrogates. The compounds have been synthesized in the present work by functionalization of the double bonds of N-substituted 6H-[1,2]oxazin-3-ones, which are obtained upon successive reaction of the triflates of S-α-hydroxy esters with O-allylhydroxylamine and acryloyl chloride, followed by cyclization of the resulting R-α-N-acryloyl-N-allyloxyamino esters in the presence of the ring-closing metathesis (RCM) catalyst bis(tricyclohexylphosphine)benzylideneruthenium dichloride. The olefins are also accessible, but less efficiently so, by a Wittig sequence that employs bromoacetyl bromide in place of acryloyl chloride, followed successively by triphenylphosphine, silver triflate, ozonolysis, and cyclization. Asymmetric dihydroxylation of these chiral olefins affords a single diastereomer in high yield having either the αR,4S,5S- or the αR,4R,5R configuration, depending on the auxiliary. The configuration of the αR,4R,5R isomer has been confirmed by its conversion to (αR,4S,5R)-2-(α-carboxyethyl)-4-phenylacetylamino-5-hydroxy-1,2-oxazinan-3-one, whose αR,4R,5S diastereomer was previously prepared from L-ascorbic acid. With N-bromosuccinimide in aqueous dimethylformamide, a 6H-[1,2]oxazin-3-one afforded a separable 1:1 mixture of bromohydrins, which could be cyclized to epoxides or hydrogenolyzed to 5-hydroxy-1,2-oxazinan-3-ones. Key words: penicillin surrogates, asymmetric dihydroxylation, bis(tricyclohexylphosphine)benzylideneruthenium dichloride, cyclic sulfite, epoxides, azidohydrin, bromohydrin.
这些标题化合物是α-氨基酸,其氮原子被包含在4,5-二取代的六元环羟肟内,它们具有潜在的β-内酰胺替代物的兴趣。这些化合物在本研究中通过N-取代6H-[1,2]噁唑-3-酮的双键官能化合成,该噁唑-3-酮是通过连续反应S-α-羟基酯的三氟甲烷酸酯与O-烯丙基羟胺和丙烯酰氯得到的,随后在环戊烯烃闭环甲硫醚催化剂双(三环己基膦)苯基亚铑二氯化物存在下,通过得到的R-α-N-丙烯酰-N-烯丙基氧基氨基酯的环化来实现。烯烃也可以通过Wittig序列获得,但效率较低,该序列使用溴乙酰溴代替丙烯酰氯,然后依次经过三苯基膦、三氟乙酸银、臭氧化、环化反应。这些手性烯烃的不对称二羟基化反应产生高产率的单对映体,具有αR,4S,5S-或αR,4R,5R构型,取决于辅助剂。αR,4R,5R异构体的构型已通过其转化为(αR,4S,5R)-2-(α-羧乙基)-4-苯乙酰氨基-5-羟基-1,2-噁唑烷-3-酮来确认,其αR,4R,5S对映体之前是由L-抗坏血酸制备的。在水合二甲基甲酰胺中使用N-溴代琥珀酰亚胺,6H-[1,2]噁唑-3-酮产生可分离的溴水合物1:1混合物,可被环化为环氧化物或氢解为5-羟基-1,2-噁唑烷-3-酮。关键词:青霉素替代物、不对称二羟基化、双(三环己基膦)苯基亚铑二氯化物、环磺酸酯、环氧化物、叠氮水合物、溴水合物。