선택한 단어 수는 입니다.
최소 단어 이상 선택하여야 합니다.
최소 단어 이상 선택하여야 합니다.
선택한 단어 수는 30입니다.
최대 10 단어까지만 선택 가능합니다.
최대 10 단어까지만 선택 가능합니다.
제안 방법
- The first study for preliminary experiments focused on the feasibility of 1 and 2 for the cyclization with achiral aldehydes promoted by a Lewis acid catalyst. To investigate the sequence outlined in Scheme 1, the cyclization began with TMS ethers 1a and 2a as starting materials.
- With the notion that this approach might lead to a general and efficient method for the synthesis of trans-2,6-dihydropyran 3, we set out to determine the substituent effects with several 10 to produce structurally various products. Indeed, the method is successful with 10 to yield the trans-2,6-disubstituted pyrans 3, in moderate to high diastereoselectivities as it can be seen in Table 2.
대상 데이터
- The α-acetoxy acetals 10 were prepared by the method described by Rychnovsky for in situ acylation of the tetrahedral intermediates generated by DIBAL reduction of corresponding esters.14 Compound 10a (R1 = PhCH2CH2, R2 = CH3) was chosen as a model compound. After surveying numerous conditions with a variety of Lewis acids, several key findings were emerged: i) reaction of 10a in the presence of (iPrO)2Ti(NTf)2 occurred readily at -78 ℃: this Lewis acid was generally superior to other Lewis aicds such as SnCl4, BF3OEt2 TMSOTf, TMSNTf2, and Me2AlNTf3; ii) 30 mol% of (iPrO)2Ti(NTf)2 required for optimal conditions in terms of chemical yields and reaction rates; iii) reaction performed at -78 ℃ in CH2Cl2 resulted in the best chemical yields and stereoselectivities in comparison with other solvents such as toluene, THF, and PhCF3； iv) diastereomeric ratio turned out to be 91 : 9 as determined by the analysis of 1H NMR of crude products.
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