The first hybrid crown ether with two adjacent disilane fragments was synthesized through reaction of O(SiMeCl) (3) with O(CHOH). By means of DFT calculations, the complexation ability of 1,2,4,5-tetrasila[12]crown-4 (7) towards Li was determined to be considerably higher compared to [12]crown-4.

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Stiirting r r t m nitro:ilk;inc ;idducts of thc gcncral siructurc 3. sew-MI versions of the N d reaction are prformcd. Thc rcagoni comhiiiuticm HIOI KICOI turncd out to bc thc most uscful in libci-iiting thr c;irhonyl group bccausc of tcilrratiori of acid-scnsitive f i i t i~t i~~r~a l i t i c s .Other methods provide the acetiil 5. diketonc 7. y-hctoncs II and 9. o r the chlurinatcd niiro compound 13, rospc- In the preceding paper'' we reported on the eficient and very flexible synthesis of polyfunctional nitroalkanes 3. These were prepared by Michael addition of simple or already functionalized nitro compounds to the vinyl ketone 2, whose precursor is siloxycyclopropane 1. This protocol allows a very convenient creation of selectively functionalized carbon chains. Since the ultimate purpose of this concept is syntheses of building blocks for natural products, the transformation of the nitro group into a carbonyl or a hydroxy function is demanded. The distinction of these oxygen functions is an unalterable prerequisite in this process. 3Almost classical Nef conditions 5, employing sodium methoxide followed by application of concentrated sulfuric acid in methanol transform the nitroalkane 4 into the acetal 5 in high yield (Scheme I), whereas compound 6 gives the diketo ester 7 containing approximately 8 % of the methanol adduct of 2. Apparently, Nef reaction is fast and succeeded by acetalization in the case of the primary nitro compound 4. In contrast, retro-Michael reaction occurs to some extent with the secondary nitroalkane 6 providing 2 and its sub- sequent addition product with methanol. Protection of the keto function in 6 allows the C -NOz + C = 0 conversion without retro-Michael addition. However, the acetal moiety is cleaved by acid in the second step, and the yield of isolated 7 is only 54%.

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