Synthesis of Silyl Enol Ethers and Their Aldol Reaction Utilizing 2,5-Dimethyl-1-silacyclopentane and 2,5-Diphenyl-1-sila-3-cyclopentene Derivatives.

Synthesis of novel silyl enol ethers from chlorodimethyl(naphthylphenylmethyl)silanes having a chiral centre and a ketone and their chirality transfer effects in crossed-aldol reactions

“…The Grignard reagent generated from 1-bromonaphthalene (10) was coupled with benzyl chloride in the presence of Pd(PPh 3 ) 4 to produce 1-benzylnaphthalene (11) compound generated from naphthalene 11 with n-BuLi was then treated with dichlorodimethylsilane to produce the corresponding racemic chlorodimethyl(1-naphthylphenylmethyl)silane ((±) 8) in 92% yield. When the racemic-(±) 8 was reacted with (S)-( + )-methylmandelate (12) in the presence of imidazole in DMF at room temperature, the expected [(1'S)-(methoxycarbonyl)phenylmethoxy]dimethy (1-naphthylphenylmethyl)silane ( 13) was obtained in 87% products, we recrystallised the diastereomeric mixture 13 twice using solvent mixtures comprised of hexane and EtOAc R,1'S)-[(methoxycarbonyl)phenylmethoxy]dimethy(1-naphthylphenylmethyl)silane (14 of 14 was unambiguously determined to be the R-form of the diastereomer using X-ray structure analysis, as shown in 14 was 4.6% and the method, [13][14][15] was used to treat the silyl ether 14 with acetyl chloride in the presence of ZnCl 2 , the desired chiral (2R)-(-)chlorodimethyl(1-naphthylphenylmethyl)silane ((-) 8) was produced in 87% yield.…”

“…Previously, we developed two novel silyl enol ethers 5 and 6, with a 2,5-dimethyl-1-phenyl-1-silacyclopentane 6 unit and a 2,5-diphenylsilacyclopent-3-ene [7][8][9][10][11] moiety, respectively, and examined the crossed-aldol reaction of the silyl enol ethers with benzaldehyde (Scheme 1). 12 When the reaction with silyl ether 5 was performed, the corresponding aldol product 7 was obtained as a mixture of erythro and threo adducts in good yield. In contrast, the reaction using silyl enol ether 6 produced only the erythro product 7 in moderate yield.…”