硫代缩醛（酮）法
酸催化下，羰基与硫醇或者二硫醇反应生成硫代缩醛(酮)也是羰基保护常用的方法。与缩醛(酮)酸敏感性不同，硫代缩醛(酮)对酸更稳定，酸性条件下水解脱除一般无效，多采用重金属离子如Hg2+蒋敬、 Ag1+、Fe3+或其他氧化剂如NBS、I2、DDQ 或mCPBA等氧化脱除。硫代缩醛(酮)也有非环的和环状的两种，其中非环状比环状容易脱除。
相比常规缩醛(酮)，硫代缩醛(酮)更容易形成，这对一些位阻大活性低的羰基保护可能优势明显，而且其酸性条件稳定性更好，某些时候这一特性可能非常有用，但是硫代缩醛(酮)也有它自身的缺点——环境不友好。首先，脱保护过程很多时候要用到重金属氧化，比常规缩醛(酮)酸性水解条件更苛刻；为了解决这一问题，人们开发了单硫缩醛(酮)：吹笛少年
其稳定性介于缩醛(酮)和硫代缩醛(酮)之间，既可以氧化脱保护也可以酸性水解。其次，硫代缩醛(酮)形成过程中用到的小分子硫醇或者二硫醇有令人难以忍受的恶臭，这也限制了他的应用。好在有一些无臭的硫代试剂可以很好的克服这一问题如：
非环和环状硫代缩醛(酮)由羰基与硫醇或者二硫醇酸催化反应而成，由于硫醇沸点低，易挥发产生恶臭气味，所以人们更愿意使用二硫醇，故环状硫代缩醛(酮)比非环状的应用更加广泛，最具代表性的非环和环状硫代缩醛(酮)如图所示：
其形成和脱除典型操作如下：
应用举例1:
A mixture of 1,3-propanedithiol (7.50 mL, 75.0 mmol), boron trifluoride etherate (9.5 mL, 7
5.0 mmol), and glacial acetic acid (18.0 mL, 0.32 mol) in dichloromethane(125 mL) was cooled to -20 oC. To the vigorously stirred mixture was added slowly a solution of 2-methyl-2-pentenal (8.55 mL, 75.0 mmol) in CH2Cl2 (50 mL) while maintaining the temperature between -20 and -15四字游戏id oC. The reaction mixture was stirred for 1 h at -20 oC, and then siphoned into ice-cold 10% aqueous KOH solution. The temperature was maintained below 5 oC during the quench. After dilution with diethyl ether, the organic pha was parated, washed with 10% KOH, water, brine, and dried (Na2SO4). Concentration in vacuum yielded 13.9 g(99%) of the crude dithiane as a 10:1 mixture of E/Z isomers. The dithiane was ud without further purification in the next step. (H.Stephen, F. Thilo, Tetrahedron, 2011, 67, 9870)
应用举例2:
NaHCO3(6.183 g, 73.6 mmol) and I碌碡怎么读食用油保质期多长时间2 (9.209 g,36.3 mmol) were added to a solution of dit
hiane (3.34 g,11.0 mmol) in aqueous acetone (94 mL of acetone plus 17 mL water). The resulting mixture was stirred at 0 o分享交流C for 30 min until TLC showed complete disappearance of starting material. The reaction was quenched with saturated aqueous Na2S2O3 and the mixture was diluted with Et人体油画艺术2旅游要带什么O. The phas were parated and the aqueous layer was extracted with Et2O. The combined organic layers were washed with saturated aqueous Na2S2O3, water, and brine, dried over Na2SO4, and concentrated on a rotary evaporator. The residue was purified by column chromatography on silica gel (2:1n-hexane/EtOAc) to give ketone as a yellowish oil (3.892 g, yield 83%). (H-X.Jin, Q. Zhang, H-S. Kim, Tetrahedron, 2006, 62, 7699)
