ISOPROPYLIDENE COMPOUNDS

The most interesting ethylene oxide derivative of the hexitols encountered hitherto is 1,2 5,6-dianhydro-D-mannitol. This was obtained in the form of its 3,4-isopropylidene (LXXXVIII) and 3,4-ethylidene (LXXXIX) derivatives.72 The isopropylidene compound was synthesized from l,6-dichloro-l,6-didesoxy-D-mannitol through its conversion first into l,6-dichloro-l,6-didesoxy-3,4-isopropylidene-D-mannitol. This,... 

Isopropylidene Compounds. Ozonolysis of any compound containing an isopropylidene group may yield the highly explosive trimeric acetone peroxide.14... 

Surprisingly, the active inositols and epf-inositol yield tri-O-isopropyli-dene acetals as well as di-O-isopropylidene compounds. The third isopro-... 

In the first route, methylbutenol is made from acetone and acetylene followed by hydrogenation. Reaction with methyl isopro-penyl ether yields methylheptenone (6). The second route involves the reaction of isobutylene, formaldehyde and acetone (7 ). Methyl vinyl ketone is an intermediate. Finally, methylheptenone is made by alkylation of acetone with prenyl chloride which is derived from isoprene (8). The initial product is the terminal olefin which is isomerized to the desired isopropylidene compound. 

Iodo-desoxy derivatives of methylene, benzylidene and isopropylidene compounds have been transformed into their desoxy analogues with Raney nickel and hydrogen in basic media (e.g. hydroxides, methoxides and diethylamine). 0 47,60,81,82 Under similar conditions, l,3 2,4-diben-zylidene-5,6-sorbitoleen has been hydrogenated 8 and 2,4-benzylidene-6-nitro-6-desoxy-D-sorbitol has been converted into the corresponding amine.84 We are not aware of any report in this field of the removal of a benzylidene group by Raney nickel, as is the case with certain sugar derivatives.88... 

If, in an attempt to obtain free 6-amino-6-deoxy-L-xt/Io-hexulose, the isopropylidene compound 80 is hydrolyzed at 65° with 2 M hydrochloric acid, an almost quantitative yield of 3-hydroxy-2-pyrldinemeth-anol (86) hydrochloride is obtained instead. The formation of 86 can result only through the intermediate 6-amino-6-deoxy-L-xyfo-hexulo-pyranose (83). The furanose (81) first formed is in equilibrium with the pyranose (83). The latter is dehydrated in acid solution to 82 which, under acid catalysis, rearranges to the intermediate 84. In the following steps, the allylic hydroxyl groups on C-4 and C-5 are readily removed, and aromatization to the pyridine derivative (86) ensues. 

The C-4 position of maltose can be modified in a similar way. Maltose, being a reducing sugar, usually has to have C-1 protected. C-1 is often protected by forming the 1,2-0-isopropylidene derivative. It has been obtained in a 33% yield and represented one of four isopropylidene compounds that were formed [111]. These compounds had to be separated on a silica-gel column. The 1,2-isopropylidene maltose is then reacted with 1,1-dimethoxy benzaldehyde to give the 4, 5 -benzili-dene derivative (reaction 4.116). The other free hydroxyl groups are protected by benzoylation, and the C-4 -0 bond is selectively cleaved to produce the free C-4 ... 

Ketones are converted to dibromomethylene derivatives. These intermediates can be transformed to isopropylidene compounds by reaction with Lithium Dimethylcuprate and lodomethane (eq 14). No racemization was reported for the chain extension... 

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