Efficient and practical asymmetric synthesis of the taxol C-13 side chain, N-benzoyl-(2R,3S)-3-phenylisoserine, and its analogs via chiral 3-hydroxy-4-aryl-.beta.-lactams through chiral ester enolate-imine cyclocondensation

Abstract

1681the simultaneous 1,5 H migration unnecessary. The interactions of BTF with isobutenyl, methallyl, and allyl ethers (and sulfides)* present the second extreme; only the bond HC(CF3), is established in the first step, and the same allylic ion pair is reached from positional isomers. BTF reactions with 1,3-diarylpropenes and benzylic H follow the same course.8 Between these two extremes, BTF combines both functions in a wide range of ene reactions.The rate constant for the reaction of ethyl methallyl ether with BTF is only little dependent on solvent polarity;2 some modifications to the one-step hydride transfel.3 were discussed: H atom transfer giving a radical pair or, in combination with SET, a radical ion pair as intermediate. Although we do not favor these alternatives, they cannot be ruled out on the basis of the substituent effects on the regiochemistry of ene reaction described here.Summary: A highly efficient chiral ester enolate-imine condensation giving 3-hydroxy-4aryl-j3-1actams with >96% ee is successfully applied to the asymmetric synthesis of the enantiomerically pure taxol C-13 side chain, Nbenzoyl-(2R,3S)-3-phenylisoserine, and i b r analogues.

Diastereoselective synthesis of trans-trifluoromethyl-β-lactams and α-alkyl-β-trifluoromethyl-β-amino esters

“…The exclusive formation of the cis-b-lactams was rationalized by the selective generation of the Elithium enolate and a ZimmermaneTraxler transition state. 41 However, Guanti and co-workers obtained exclusively a trans-b-lactam by cyclocondensation of N-(2,2,2-trifluoroethylidene)-4-methoxyaniline with the lithium enolate of N,N-dibenzyl ethylglycinate. In this case, the Z-enolate is favored leading to the trans-b-lactam.…”

Medicinal Chemistry of α‐Hydroxy‐β‐Amino Acids

“…Starting from sililoxyacetate 43, bearing (-)-trans-2-phenyl-1-cyclohexanol as a chiral auxiliary, and N-(p-methoxyphenyl)aldimine 44, stereoselective synthesis of b-lactam 45 was achieved. This compound was then hydrolyzed to (2R,3S)-phenylisoserine (Scheme 6.8c) [39,40]. This method can be easily modified to afford other a-hydroxyl-b-amino acids [41].…”

Efficient purification of paclitaxel from yews using high-performance displacement chromatography technique

“…As a result, over the past decades, renewable biomass of yew such as needles, twigs, and/or stems has been recognized as a valuable source of paclitaxel and its several semi-synthetic precursors having the same core skeleton. Numerous attempts to develop an economical and reliable alternative method for paclitaxel and docetaxel production have also been made, including chemical and semisynthesis [14,15], totalsynthesis [16,17], and the cell culture [18][19][20].…”