Boron trifluoride etherate

Abstract

Shan et al. 2 showed that it BF 3OEt 2 is useful for the preparation of a variety of substituted quinolines some of which are difficult to make via conventional approaches. An efficient one-step [3+3] annulation reaction at room temperature between 3-ethoxycyclobutanones and aromatic amines is realized. The reaction shows excellent reactivity, good functional group tolerance, complete regioselectivity, and high yields. Kouznetsov and co-workers3 reported an efficient, easy, fast, and cheap way for the synthesis of the new spiro dihydroquinolineoxindoles using the Povarov reaction. This method use BF 3.OEt 2 for promoted imino-DielsAlder cycloaddition between ketimine-isatin derivatives and trans-isoeugenol. Aldehydes undergo smooth cyclization with 4-(phenylthio)but-3- en-1-ol in the presence of BF 3.OEt 2 to afford a novel class of 2,3-disubstituted tetrahydrofurans in good yields with all-cis-selectivity. 4 This method is simple, selective, and convenient, that provides a variety tetrahydrofurans in a single-step operation. Subba et al.9 have developed a novel approach for the synthesis of 5,7-diarylhexahydro-2H-furo[3,2-b]pyrans via Prins FriedelCrafts cyclization. In this reaction a D-glucose-based homoallylic alcohol reacts smoothly with various aldehydes in the presence of arenes and a catalytic amount of BF3OEt2 under mild conditions. This method provides an easy access for a new class of annulated pyran sugars in a single-step operation, which may find application in drug discovery and also in natural products synthesis. BF 3.OEt 2 promotes ring opening of vinylidenecyclopropanes which reacts with xanthydrol to give the corresponding conjugate triene derivatives in moderated to good yields.5 Interesting transformation of these conjugate trienes has been disclosed in the presence of BF 3.OEt 2 at 70 °C, affording a series of novel spiro-alkanes in moderate to good yields. Jha et al.1 described the first example of a chemoselective S-benzylation of indoline-2-thiones under mild conditions, using a variety of benzyl alcohols and BF3OEt2. In this procedure the aryl substituent has effects on the reactivity of benzyl alcohols toward S-benzylation and the results of those effects were also discussed. Machin and Pagenkopf reported that in the presence of BF 3.OEt 2 cyclobutane-1,1-diesters undergo a reaction with terminal alkynes to a quickly access to dihydro-oxepines.10 These oxepines are formed through an intriguing rearrangement sequence. This methodology is currently being investigated for potential application towards the formation of fully saturated oxepines and the total synthesis of natural products. Kokubo et al. showed that BF 3.OEt 2 promotes dehydrative cycloaddition reaction of benzoquinones with stilbene oxides to afford benzofurans and dihydrobenzofurans in good combined yields.6 Petrov and Marshall developed the reaction of 2,2-bis(trifluoromethyl)-4-oxoetanes with BF 3.OEt 2 in CH 2Cl 2 as solvent which results a spontaneous electrophilic [4+4] cyclodimerization with the formation of the corresponding dioxocanes isolated in 3142% yield. 7. © Georg Thieme Verlag Stuttgart · New York.