Aldehydes, with functional heteroatom group

Tab. 6.2. Syntheses of alkenes by intermolecular McMur reactions of aldehydes and ketones with functional heteroatom groups.

Assuming that a carbonyl compound 1 with a substituent Y (which may be either a heteroatomic substituent or an alkyl group) forms enolate 2 exclusively, and that the aldehyde 3 functions as the only carbonyl-active component12, four stereoisomeric products 4a, 4b, 5a, 5 b may result. 

In order to avoid this unfavourable effect of the functional groups in the dendrimer structure, a rigid hydrocarbon backbone without heteroatoms was synthesized. Dendrimers with poly(phenylethyne) backbones, bearing three and six ephedrine derivatives at the periphery, were studied in the alkylation of aldehydes and N-diphenylphosphinylimines and proved to be highly en-antioselective catalysts. For example, the system containing six catalytic sites catalyzed the addition of diisopropylzinc to aldehydes with enantioselectivi-ties of up to 86% ee. As a third backbone a polycarbosilane dendrimer was used, which is chemically inert and more flexible than the poly(phenylethyne)... 

An unexpected reactivity in the functionalization of 2-acyl-l,3-dithianes has been reported by Mioskowski and co-workers. They found that 2-acyl-l,3-dithianes with no further heteroatom at the acyl side chain react with aldehydes to give 2-acyl-2-hydroxyalkyl-l,3-dithianes, whereas a silyl-protected hydroxy group in the side chain of the 2-acyl-l,3-dithiane led to formation of the aldol product at the opposite site of the carbonyl group. Acyl chlorides always react with 2-acyl-l,3-dithianes to give the enol esters (Scheme 81) <2003TL213>. 

The label 1,1-diX may look strange but all it means is that the two functional groups are joined to the same carbon atom. You already know how to make acetals 68 you combine an aldehyde 67 with an alcohol, say methanol, in acidic solution. The disconnection 68a is therefore of both C-0 bonds. This reveals a valuable truth two heteroatoms joined to the same carbon atom are at the carbonyl oxidation level (two C-0 bonds to the same C atom in both 67 and 68) and the TM is probably made from a carbonyl compound. 

Functionalized allyltributylstannanes can also be used in the BINOL/Ti-cata-lyzed reaction and addition of P-substituted allyl groups with heteroatoms in the side chain to aldehydes has been achieved with a high degree of enantiocon-trol [ 16]. The catalytic asymmetric allylation has been successfully applied to to -tal syntheses of the macrohdes (l )-(-i-)-ricinelaidic acid lactone and (-)-gloe-osporone [21]. 

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