Stereoselective synthesis of 4-alkoxy-3-methylidenealkanols using reactions between 2-(1-alkoxyalkyl)propenylstannanes and aldehydes: X-ray crystal structure of (1R,4R)-3-methylidene-1-(4-nitrophenyl)pentane-1,4-diol
作者:Pedro Almendros、Michelangelo Gruttadauria、Madeleine Helliwell、Eric J. Thomas
DOI:10.1039/a702256e
日期:——
The 2-(1-hydroxy- and 1-alkoxy-alkyl)propenylstannanes 9 and
11–15, react with aldehydes to form 4-hydroxy- and
4-alkoxy-3-methylidenealkanols 23, 24 and 36–53. The
stereoselectivity of these reactions has been investigated. If the
reactions are carried out by transmetallation of the stannane using a
tin(IV) halide before addition of the aldehyde, modest
stereoselectivity in favour of the 1,4-anti-products 23, 36 and
37 is observed for the hydroxystannane 9, whereas the alkoxystannanes
11–15 give rise preferentially to the
1,4-syn-diastereoisomers 47–53, selectivity
75–85∶25–15. It should be noted that these
stereochemical assignments are the reverse of those reported in the
preliminary communication on this work. The structure of the
1,4-anti-product 36 from the reaction between the
hydroxystannane 9 and p-nitrobenzaldehyde was established by
X-ray diffraction. The stereoselectivity of
BINOL–titanium(IV) catalysed reactions of the
(R)-SEM-stannane (R)-12 with benzaldehyde is
controlled by the configuration of the BINOL and can be used to
synthesize either the 1,4-anti- or 1,4-syn-isomers 40
and 47.
2-(1-羟基-和1-烷氧基-烷基)丙烯基锡化合物9和11–15与醛反应生成4-羟基-和4-烷氧基-3-亚甲基烷基醇23、24和36–53。这些反应的立体选择性已被研究。如果反应通过锡化合物的转移金属化作用,使用四价锡卤化物,然后再加入醛进行反应,对于羟基锡化合物9,观察到适度的立体选择性,偏向于1,4-反式产物23、36和37,而烷氧基锡化合物11–15则优先生成1,4-顺式非对映异构体47–53,选择性为75–85∶25–15。值得注意的是,这些立体化学的指定与初步通讯中报道的情况相反。通过X射线衍射确定了羟基锡化合物9与对硝基苯甲醛反应生成的1,4-反式产物36的结构。BINOL-钛(IV)催化的(R)-SEM-锡化合物(R)-12与苯甲醛反应的立体选择性受BINOL构型的控制,可用于合成1,4-反式或1,4-顺式异构体40和47。