L-aza-2-silacyclobutanes

The [2 + 2] cycloreversion of l-aza-2-silacyclobutanes (silaazetidines) is a possible mode of silanimine preparation (equation 229). 

Remarkable dependence of the regioselectivity on the catalyst species employed is observed in the intramolecular hydrosilylation of allylic /V-dimethylsilylamines 63, i.e. the Rh-catalyzed reactions proceed via 5-endo cyclization to give l-aza-2-silacyclopentanes 64 whereas the Pt-catalyzed reactions yield l-aza-2-silacyclobutanes 65 via A-exo... 

The 4-exo cyclization of open-chain substrates 63 proceeds in trans-fashion with moderate to excellent selectivity (trans/cis = 77/23 > 99/1 )90. The trans selectivity is dependent on the substitution pattern of R2, R3 and R4. The reactions giving trans-l-aza-2-silacyclobutanes 65 have been applied to the stereoselective syntheses of syn-amino alcohols 66 via the Tamao oxidation as exemplified by the reaction of 63d (R = HMe2Si), affording 66d (76% overall yield in 4 steps, syn/anti = > 99/1) via 65d (trans/cis = > 99/1) in equation 2690. In the case of 3-iV-disilylamino-l-cyclohexene 63f (R = HMe2Si), however, cis-l-aza-2-silacyclobutane 65f is formed exclusively, that is converted to ds-2-amino-l-cyclohexanol (66f) (equation 27)90. 

Aryl isocyanides insert in the Si-Si bond in bicyclic 1,2-di-silacyclobutanes (93JOM35). Macrocyclic compounds containing two l-aza-3-silacyclobutane rings have been prepared and an X-ray crystal structure obtained (93CC1585). 

Symmetrical l,3-diaza-4-silacyclobutane 15 was formed in a [2+2] cycloaddition of the Si=N double bond of the iminosilane 102 across the C=N double bond of phenylisocyanate (Scheme 25). However, treatment of the silane mentioned above with /< +-butylisocyanate afforded l-aza-3-oxa-4-silacyclobutane 52 possessing the exocyclic C=N double bond. The compound 51 is the product of the reaction of iminosilane with 2-methylpropenal <1996JOM(515)43>. 

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