Concise synthesis of valuable chiral N -Boc- β -benzyl- β -amino acid via construction of chiral N -Boc-3-benzyl-5-oxoisoxazolidine through cross-metathesis/conjugate addition/oxidation

Transformations of bio‐sourced 4‐hydroxyphenylpropanoids based on olefin metathesis

“…The o-allylphenol (83) was thus reacted with benzyl hex-5enoate (84) in two steps in the presence of 1 and then 4 mol% of Ru13 in THF at 22°C to produce (86) in 63 % isolated yield with excellent (Z)-stereoselectivity (Scheme 21). [61] With the same strategy, chavicol (4) and methyl eugenol (5) were transformed into the corresponding allyl alcohol derivatives (87)- (89) in the presence of 1 and then 5 mol% of Ru14 at 22°C using (Z)-butene (85) as methylene capping agent and (Z)-2-methyl but-2-enol or its benzyl ether as coupling partner (Scheme 22).…”

“…Thus, the one-pot cross metathesis in the presence of 0.1 mol% of Ru2 in refluxing dichloromethane followed by organocatalytic conjugate addition with N-BocNHOH at 0°C in the presence of p-nitrobenzoic acid and (S)-diphenylprolinol-TMS produced the (3R)-tert-butyl 3-arylmethyl-5-hydroxyisoxazolidine carboxylate (130) in 75 % yield with 85 % enantioselectivity. [86] Further oxidation of the hydroxy group of (130) by NaClO 2 /H 2 O 2 followed by hydrogenolysis of the NÀ O bond by dihydrogen catalysed by palladium gave the optically active β-amino acid derivative (131).…”

Practical Asymmetric Synthesis of Sitagliptin Phosphate Monohydrate

“…In the last decades, a variety of chiral amino acids can be made from hemiacetals through catalytic tandem aza-Michael/hemiacetal reaction, using organocatalyst in high yield and enantioselectivity [ 15 , 16 , 17 , 18 , 19 ]. As part of our efforts to develop efficient and practical access to stigliptin phosphate monohydrate, we herein report an efficient synthetic route to make sitagliptin phosphate monohydrate by means of chiral hemiacetal as the key intermediate.…”