Dichloromethane, lithio

Lithio-l-methoxycyclopropane can be generated by reductive lithiation of 1-methoxy-l-phenylsulfanylcyclopropane with lithium 1-dimethylaminonaphthalenide (Method A)146,147 or lithium 4,4 -di-f< r/-butylbiphenylide (Method B)148 in tetrahydrofuran at — 78 °C. 1-Lithio-l-methoxycyclopropanc reacts with enones and enals to produce 1-methoxycyclo-propanemethanols, which rearrange to vinylcyclobutanones 1 using tetrafluoroboric acid in tetrahydrofuran (Method C) 146,147 or triflic anhydride in the presence of 2,6-di-f 77-butyl-4-methylpyridine in dichloromethane (Method D).148 The latter method avoids destruction of acid-sensitive products (Table 11). 

The dithiane derivative 60 (Scheme 14) is such a compound, it being made from 2,3 5,6-di-0-isopropylidene-D-mannose by treatment with 2-lithio-l,3-dithiane to give a heptose dithioacetal that was refunctionalized at C-2-C-3 by way of the C-l anion and then converted to the 6,7-epoxide following selective acid-catalyzed cleavage of the 6,7-acetal ring. Treated with n-butyllithium it gives, in 70% yield, the cyclized 61, which is efficiently convertible into validatol 62, a component of validamycin A, by desulfurization with Raney nickel and de-O-protection by use of boron tribromide in dichloromethane [31]. 

MCPBA in dichloromethane (DCM) continues to be used as an oxidant for the preparation of benzo-l,5-dioxapins <2001S473, 1996SC4459>. Dibenzothiins and phenoxathiins undergo DTBB-catalyzed lithiation (DTBB - 4,4 -di-fert-butylbiphenyl). Reaction of the so-formed lithio intermediates with suitable electrophiles gives 29, which undergoes cyclization (Scheme 12) <2002CL726>. 

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