Pyranoside homologation

C. Burnouf, J. C. Lopez, M. de los A. Laborde, A. Olesker, and G. Lukacs, An efficient route to homologated pyranosidic conjugated enals, Tetrahedron Lett., 29 (1988) 5533-5534. 

Homologated a-Enal Pyranosides as Heterodienes. An a,P-unsaturated aldehyde can also behave as an 1-oxabutadiene system (25). The resulting compound will be an "homologated pyranoside" (26) (term coined by Fraser-Reid (27) to describe two linked pyranoside units) and such compounds are useful synthons for multichiral arrays (28). 

Other methods have been reported which, however, lacked generality. One of these described the approach to L-g/ycera-D-manno-heptopyranosides by stereoselective chain extension of suitably protected hexodialdo-l,5-pyranosides with silylmethylmagnesium chlorides [31]. Another method, quite reminiscent of the Masamune-Sharpless approach [7g], reported the synthesis of four stereoisomeric tetrose derivatives by homologation of... 

B. Fraser-Reid, L. Magdzinski, and B. Molino, New strategy for carbohydrate-based syntheses of multichiral arrays pyranosidic homologation. 3, J. Am. Chem. Soc., 106 (1984) 731-734. 

Molino, B F, Magdzinski, L, Fraser-Reid, B, Pyranosidic homologation Part I extending the carbohydrate template via C-6 and C-4 + Part II, Tetrahedron Lett., 24, 5819-5822, 1983. 

Mootoo, D R, Fraser-Reid, B, The nine contiguous chiral centers in streptovaricin A via pyranosidic homologation, J. Org. Chem., 54, 5548-5550, 1989. 

The pyranosidic homologation strategy has been also applied to the synthesis of compound (114) [196a,b], which also contains the nine stereocenters of streptovaricin A ansa chain (Scheme 50). Compound (114) was prepared starting from a D-glucose derivative, after conversion into a dipyranoside [196a] and thence tripyranoside [196d]. 

J. C. Lopez, E. Lameignere, C. Bumouf, M. de Los Angeles Laborde, A. A. Ghini, A. Olcsker, and G. Lukacs, Efficient routes to pyranosidic homologated conjugated enals and dienes from monosaccharides. Tetrahedron 49 7701 (1993). 

We therefore go from a mono- to di- to trip3nranoside (11 —> 12 —> 13) in a process which we have defined as "pyranosidic homologation" (ref 15). The tripyranoside 13 can accommodate eight of the nine chiral centers of 4 on the three p3n"anoside rings. 

These two observations meant that the twin advantages of pyranosidic homologation, namely, stereocontrol and structure proof which were declared as our initial objective had been fulfilled. 

Homologated a-Enal Pyranosides as Dienophiles. 2,3-Enal pyranoside 19 reacted with an excess of butadiene in CH2CI2 in the presence of AICI3 as catalyst at -78°C to give carbocyclic compound 32 (Figure 10a) (8) as a sole stereoisomer in 75-... 

Further work on "pyranoside homologation" has illustrated its use in producing compounds with multiple chiral centres. Epoxide (106) was transformed via (107) into the dipyranosides (108) and... 

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