Table 1.

Optimization of the MAP reaction with acetals

Entry	Lewis Acida	Base (equiv)	Temp	Solvent	Yield	dr (X) eq:axb	dr (OMe)c
1d	TiBr4	None	−78 °C	CH2Cl2	43%	86:14	55:45
2d	TiBr4	iPr2NEt (1.5)	−78 °C	CH2Cl2	29%	82:18	55:45
3	TiBr4	2,6-DBMP (1.5)	−78 °C	CH2Cl2	67%	92:8	55:45
4	TiBr4	2,6-DBMP (1.5)	−78 °C	CH2Cl2/hexanes	44%	93:7	55:45
5	TiBr4/Ti(OiPr)4e	2,6-DBMP (1.5)	−78 °C	CH2Cl2	50%	91:9	53:47
6	TiCl4	2,6-DBMP (1.5)	−78 °C	CH2Cl2	44%	90:10	57:43
7	TMSBr	2,6-DBMP (1.5)	0 °C	CH2Cl2	0%	–	–
8	AlBr3f	AlMe3 (0.3)	−40 °C	CH2Cl2	40%	80:20	56:44

^aUnless otherwise noted, 4 equiv of Lewis acid was used.

^bDetermined by integration of the crude ¹H NMR spectra.

^cDetermined by GC analysis.

^d17% of THP 16 was also isolated.

^eFormed by pre-mixing an 8:1 solution of TiBr₄ and Ti(OⁱPr)₄.

^f1.5 equiv of AlBr₃.